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 $54.44   9.779%   $59.7637   $59.76   $59.75   $59.80  
  Purchase #2 $199.76   6.201%   $212.1471   $212.15   $212.15   $212.10  
  Purchase #3 $246.67   8.104%   $266.6601   $266.66   $266.65   $266.70  
  Purchase #4 $164.92   11.243%   $183.462   $183.46   $183.45   $183.50  
  Purchase #5 $233.74   5.625%   $246.8879   $246.89   $246.90   $246.90  
  Purchase #6 $113.29   7.498%   $121.7845   $121.78   $121.80   $121.80  
  Purchase #7 $75.78   11.309%   $84.35   $84.35   $84.35   $84.40  
  7 purchase totals = $1,088.60       $1,175.0553   $1,175.05   $1,175.05   $1,175.20