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 $210.93   7.536%   $226.8257   $226.83   $226.85   $226.80  
  Purchase #2 $193.87   8.392%   $210.1396   $210.14   $210.15   $210.10  
  Purchase #3 $211.40   7.663%   $227.5996   $227.60   $227.60   $227.60  
  Purchase #4 $151.87   8.352%   $164.5542   $164.55   $164.55   $164.60  
  Purchase #5 $80.95   9.112%   $88.3262   $88.33   $88.35   $88.30  
  Purchase #6 $167.97   10.800%   $186.1108   $186.11   $186.10   $186.10  
  Purchase #7 $33.38   13.131%   $37.7631   $37.76   $37.75   $37.80  
  7 purchase totals = $1,050.37       $1,141.3192   $1,141.32   $1,141.35   $1,141.30