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 $48.75   12.225%   $54.7097   $54.71   $54.70   $54.70  
  Purchase #2 $167.59   4.790%   $175.6176   $175.62   $175.60   $175.60  
  Purchase #3 $201.59   4.817%   $211.3006   $211.30   $211.30   $211.30  
  Purchase #4 $63.33   8.317%   $68.5972   $68.60   $68.60   $68.60  
  Purchase #5 $118.63   10.759%   $131.3934   $131.39   $131.40   $131.40  
  Purchase #6 $235.64   7.198%   $252.6014   $252.60   $252.60   $252.60  
  Purchase #7 $227.58   13.226%   $257.6797   $257.68   $257.70   $257.70  
  7 purchase totals = $1,063.11       $1,151.8996   $1,151.90   $1,151.90   $1,151.90