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 $168.50   9.533%   $184.5631   $184.56   $184.55   $184.60  
  Purchase #2 $75.84   10.341%   $83.6826   $83.68   $83.70   $83.70  
  Purchase #3 $186.44   9.406%   $203.9765   $203.98   $204.00   $204.00  
  Purchase #4 $95.88   4.538%   $100.231   $100.23   $100.25   $100.20  
  Purchase #5 $179.40   5.332%   $188.9656   $188.97   $188.95   $189.00  
  Purchase #6 $205.54   11.525%   $229.2285   $229.23   $229.25   $229.20  
  Purchase #7 $239.51   9.810%   $263.0059   $263.01   $263.00   $263.00  
  7 purchase totals = $1,151.11       $1,253.6532   $1,253.66   $1,253.70   $1,253.70