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 $47.31   12.242%   $53.1017   $53.10   $53.10   $53.10  
  Purchase #2 $213.53   6.163%   $226.6899   $226.69   $226.70   $226.70  
  Purchase #3 $152.32   6.739%   $162.5848   $162.58   $162.60   $162.60  
  Purchase #4 $108.46   12.814%   $122.3581   $122.36   $122.35   $122.40  
  Purchase #5 $228.68   6.333%   $243.1623   $243.16   $243.15   $243.20  
  Purchase #6 $107.99   7.173%   $115.7361   $115.74   $115.75   $115.70  
  Purchase #7 $125.25   10.277%   $138.1219   $138.12   $138.10   $138.10  
  7 purchase totals = $983.54       $1,061.7548   $1,061.75   $1,061.75   $1,061.80