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 $62.41   11.518%   $69.5984   $69.60   $69.60   $69.60  
  Purchase #2 $37.79   4.393%   $39.4501   $39.45   $39.45   $39.50  
  Purchase #3 $6.94   6.401%   $7.3842   $7.38   $7.40   $7.40  
  Purchase #4 $250.56   6.644%   $267.2072   $267.21   $267.20   $267.20  
  Purchase #5 $20.85   9.531%   $22.8372   $22.84   $22.85   $22.80  
  Purchase #6 $113.31   4.741%   $118.682   $118.68   $118.70   $118.70  
  Purchase #7 $139.67   12.139%   $156.6245   $156.62   $156.60   $156.60  
  7 purchase totals = $631.53       $681.7836   $681.78   $681.80   $681.80