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 $68.51   10.334%   $75.5898   $75.59   $75.60   $75.60  
  Purchase #2 $106.78   12.304%   $119.9182   $119.92   $119.90   $119.90  
  Purchase #3 $45.70   11.428%   $50.9226   $50.92   $50.90   $50.90  
  Purchase #4 $207.56   12.213%   $232.9093   $232.91   $232.90   $232.90  
  Purchase #5 $107.88   6.440%   $114.8275   $114.83   $114.85   $114.80  
  Purchase #6 $97.61   13.609%   $110.8937   $110.89   $110.90   $110.90  
  Purchase #7 $153.96   12.113%   $172.6092   $172.61   $172.60   $172.60  
  7 purchase totals = $788.00       $877.6703   $877.67   $877.65   $877.60