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 $169.73   13.763%   $193.0899   $193.09   $193.10   $193.10  
  Purchase #2 $94.37   4.274%   $98.4034   $98.40   $98.40   $98.40  
  Purchase #3 $141.77   8.300%   $153.5369   $153.54   $153.55   $153.50  
  Purchase #4 $216.25   3.573%   $223.9766   $223.98   $224.00   $224.00  
  Purchase #5 $59.84   9.243%   $65.371   $65.37   $65.35   $65.40  
  Purchase #6 $35.31   12.173%   $39.6083   $39.61   $39.60   $39.60  
  Purchase #7 $25.96   6.644%   $27.6848   $27.68   $27.70   $27.70  
  7 purchase totals = $743.23       $801.6709   $801.67   $801.70   $801.70