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 $245.92   7.651%   $264.7353   $264.74   $264.75   $264.70  
  Purchase #2 $52.96   5.553%   $55.9009   $55.90   $55.90   $55.90  
  Purchase #3 $73.48   3.773%   $76.2524   $76.25   $76.25   $76.30  
  Purchase #4 $191.87   5.209%   $201.8645   $201.86   $201.85   $201.90  
  Purchase #5 $79.50   11.748%   $88.8397   $88.84   $88.85   $88.80  
  Purchase #6 $27.71   3.429%   $28.6602   $28.66   $28.65   $28.70  
  Purchase #7 $43.77   3.555%   $45.326   $45.33   $45.35   $45.30  
  7 purchase totals = $715.21       $761.5790   $761.58   $761.60   $761.60