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 $59.78   12.111%   $67.02   $67.02   $67.00   $67.00  
  Purchase #2 $195.55   7.210%   $209.6492   $209.65   $209.65   $209.60  
  Purchase #3 $175.50   12.688%   $197.7674   $197.77   $197.75   $197.80  
  Purchase #4 $178.39   7.504%   $191.7764   $191.78   $191.80   $191.80  
  Purchase #5 $240.95   3.864%   $250.2603   $250.26   $250.25   $250.30  
  Purchase #6 $199.37   3.700%   $206.7467   $206.75   $206.75   $206.70  
  Purchase #7 $32.26   7.337%   $34.6269   $34.63   $34.65   $34.60  
  7 purchase totals = $1,081.80       $1,157.8469   $1,157.86   $1,157.85   $1,157.80