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 $82.38   11.616%   $91.9493   $91.95   $91.95   $91.90  
  Purchase #2 $51.81   3.839%   $53.799   $53.80   $53.80   $53.80  
  Purchase #3 $116.27   11.739%   $129.9189   $129.92   $129.90   $129.90  
  Purchase #4 $127.49   4.860%   $133.686   $133.69   $133.70   $133.70  
  Purchase #5 $24.51   4.212%   $25.5424   $25.54   $25.55   $25.50  
  Purchase #6 $102.73   9.445%   $112.4328   $112.43   $112.45   $112.40  
  Purchase #7 $80.77   7.694%   $86.9844   $86.98   $87.00   $87.00  
  7 purchase totals = $585.96       $634.3128   $634.31   $634.35   $634.20