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 $63.69   7.820%   $68.6706   $68.67   $68.65   $68.70  
  Purchase #2 $153.99   9.130%   $168.0493   $168.05   $168.05   $168.00  
  Purchase #3 $26.45   6.778%   $28.2428   $28.24   $28.25   $28.20  
  Purchase #4 $106.93   13.846%   $121.7355   $121.74   $121.75   $121.70  
  Purchase #5 $121.42   7.460%   $130.4779   $130.48   $130.50   $130.50  
  Purchase #6 $216.53   3.421%   $223.9375   $223.94   $223.95   $223.90  
  Purchase #7 $20.40   6.814%   $21.7901   $21.79   $21.80   $21.80  
  7 purchase totals = $709.41       $762.9037   $762.91   $762.95   $762.80