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 $93.68   3.272%   $96.7452   $96.75   $96.75   $96.70  
  Purchase #2 $113.93   9.579%   $124.8434   $124.84   $124.85   $124.80  
  Purchase #3 $219.55   11.844%   $245.5535   $245.55   $245.55   $245.60  
  Purchase #4 $55.40   8.867%   $60.3123   $60.31   $60.30   $60.30  
  Purchase #5 $50.62   6.289%   $53.8035   $53.80   $53.80   $53.80  
  Purchase #6 $48.44   12.470%   $54.4805   $54.48   $54.50   $54.50  
  Purchase #7 $60.62   8.302%   $65.6527   $65.65   $65.65   $65.70  
  7 purchase totals = $642.24       $701.3911   $701.38   $701.40   $701.40