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 $47.94   10.401%   $52.9262   $52.93   $52.95   $52.90  
  Purchase #2 $115.65   6.399%   $123.0504   $123.05   $123.05   $123.10  
  Purchase #3 $155.56   7.727%   $167.5801   $167.58   $167.60   $167.60  
  Purchase #4 $81.50   8.517%   $88.4414   $88.44   $88.45   $88.40  
  Purchase #5 $214.99   12.376%   $241.5972   $241.60   $241.60   $241.60  
  Purchase #6 $187.71   12.694%   $211.5379   $211.54   $211.55   $211.50  
  Purchase #7 $118.63   5.799%   $125.5094   $125.51   $125.50   $125.50  
  7 purchase totals = $921.98       $1,010.6426   $1,010.65   $1,010.70   $1,010.60