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 $59.60   12.324%   $66.9451   $66.95   $66.95   $66.90  
  Purchase #2 $198.88   3.794%   $206.4255   $206.43   $206.45   $206.40  
  Purchase #3 $169.46   8.809%   $184.3877   $184.39   $184.40   $184.40  
  Purchase #4 $148.79   12.810%   $167.85   $167.85   $167.85   $167.90  
  Purchase #5 $224.85   3.191%   $232.025   $232.03   $232.05   $232.00  
  Purchase #6 $231.75   13.346%   $262.6794   $262.68   $262.70   $262.70  
  Purchase #7 $27.60   11.219%   $30.6964   $30.70   $30.70   $30.70  
  7 purchase totals = $1,060.93       $1,151.0091   $1,151.03   $1,151.10   $1,151.00