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 $235.46   13.639%   $267.5744   $267.57   $267.55   $267.60  
  Purchase #2 $125.65   12.810%   $141.7458   $141.75   $141.75   $141.70  
  Purchase #3 $67.40   10.133%   $74.2296   $74.23   $74.25   $74.20  
  Purchase #4 $230.76   11.187%   $256.5751   $256.58   $256.60   $256.60  
  Purchase #5 $119.64   4.692%   $125.2535   $125.25   $125.25   $125.30  
  Purchase #6 $189.84   5.373%   $200.0401   $200.04   $200.05   $200.00  
  Purchase #7 $213.54   11.823%   $238.7868   $238.79   $238.80   $238.80  
  7 purchase totals = $1,182.29       $1,304.2053   $1,304.21   $1,304.25   $1,304.20