Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $64.88   6.311%   $68.9746   $68.97   $68.95   $69.00  
  Purchase #2 $243.71   5.846%   $257.9573   $257.96   $257.95   $258.00  
  Purchase #3 $115.27   12.760%   $129.9785   $129.98   $130.00   $130.00  
  Purchase #4 $108.65   10.650%   $120.2212   $120.22   $120.20   $120.20  
  Purchase #5 $227.63   11.868%   $254.6451   $254.65   $254.65   $254.60  
  Purchase #6 $222.82   12.628%   $250.9577   $250.96   $250.95   $251.00  
  Purchase #7 $114.93   11.244%   $127.8527   $127.85   $127.85   $127.90  
  7 purchase totals = $1,097.89       $1,210.5871   $1,210.59   $1,210.55   $1,210.70