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 $104.45   11.746%   $116.7187   $116.72   $116.70   $116.70  
  Purchase #2 $178.41   7.282%   $191.4018   $191.40   $191.40   $191.40  
  Purchase #3 $55.90   8.387%   $60.5883   $60.59   $60.60   $60.60  
  Purchase #4 $230.30   11.270%   $256.2548   $256.25   $256.25   $256.30  
  Purchase #5 $76.86   13.595%   $87.3091   $87.31   $87.30   $87.30  
  Purchase #6 $55.89   8.531%   $60.658   $60.66   $60.65   $60.70  
  Purchase #7 $238.62   5.279%   $251.2167   $251.22   $251.20   $251.20  
  7 purchase totals = $940.43       $1,024.1474   $1,024.15   $1,024.10   $1,024.20