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 $62.92   7.270%   $67.4943   $67.49   $67.50   $67.50  
  Purchase #2 $247.47   11.593%   $276.1592   $276.16   $276.15   $276.20  
  Purchase #3 $241.32   11.340%   $268.6857   $268.69   $268.70   $268.70  
  Purchase #4 $143.94   12.375%   $161.7526   $161.75   $161.75   $161.80  
  Purchase #5 $170.78   4.611%   $178.6547   $178.65   $178.65   $178.70  
  Purchase #6 $59.66   7.175%   $63.9406   $63.94   $63.95   $63.90  
  Purchase #7 $121.89   10.405%   $134.5727   $134.57   $134.55   $134.60  
  7 purchase totals = $1,047.98       $1,151.2598   $1,151.25   $1,151.25   $1,151.40