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 $84.82   8.144%   $91.7277   $91.73   $91.75   $91.70  
  Purchase #2 $49.67   6.285%   $52.7918   $52.79   $52.80   $52.80  
  Purchase #3 $58.51   3.352%   $60.4713   $60.47   $60.45   $60.50  
  Purchase #4 $75.38   10.867%   $83.5715   $83.57   $83.55   $83.60  
  Purchase #5 $176.76   7.583%   $190.1637   $190.16   $190.15   $190.20  
  Purchase #6 $37.57   8.241%   $40.6661   $40.67   $40.65   $40.70  
  Purchase #7 $238.25   6.139%   $252.8762   $252.88   $252.90   $252.90  
  7 purchase totals = $720.96       $772.2683   $772.27   $772.25   $772.40