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 $67.35   5.384%   $70.9761   $70.98   $71.00   $71.00  
  Purchase #2 $220.91   6.717%   $235.7485   $235.75   $235.75   $235.70  
  Purchase #3 $243.45   12.538%   $273.9738   $273.97   $273.95   $274.00  
  Purchase #4 $162.65   5.377%   $171.3957   $171.40   $171.40   $171.40  
  Purchase #5 $116.91   6.625%   $124.6553   $124.66   $124.65   $124.70  
  Purchase #6 $105.87   5.651%   $111.8527   $111.85   $111.85   $111.90  
  Purchase #7 $5.36   11.577%   $5.9805   $5.98   $6.00   $6.00  
  7 purchase totals = $922.50       $994.5826   $994.59   $994.60   $994.70