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 $59.30   13.751%   $67.4543   $67.45   $67.45   $67.50  
  Purchase #2 $187.76   4.251%   $195.7417   $195.74   $195.75   $195.70  
  Purchase #3 $194.51   3.245%   $200.8218   $200.82   $200.80   $200.80  
  Purchase #4 $209.67   7.209%   $224.7851   $224.79   $224.80   $224.80  
  Purchase #5 $180.58   11.467%   $201.2871   $201.29   $201.30   $201.30  
  Purchase #6 $188.77   4.681%   $197.6063   $197.61   $197.60   $197.60  
  Purchase #7 $246.70   10.460%   $272.5048   $272.50   $272.50   $272.50  
  7 purchase totals = $1,267.29       $1,360.2011   $1,360.20   $1,360.20   $1,360.20