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 $14.41   13.406%   $16.3418   $16.34   $16.35   $16.30  
  Purchase #2 $191.81   9.631%   $210.2832   $210.28   $210.30   $210.30  
  Purchase #3 $58.30   9.860%   $64.0484   $64.05   $64.05   $64.00  
  Purchase #4 $211.60   3.333%   $218.6526   $218.65   $218.65   $218.70  
  Purchase #5 $99.26   3.137%   $102.3738   $102.37   $102.35   $102.40  
  Purchase #6 $212.63   13.351%   $241.0182   $241.02   $241.00   $241.00  
  Purchase #7 $64.96   13.595%   $73.7913   $73.79   $73.80   $73.80  
  7 purchase totals = $852.97       $926.5093   $926.50   $926.50   $926.50