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 $159.41   13.715%   $181.2731   $181.27   $181.25   $181.30  
  Purchase #2 $163.95   12.696%   $184.7651   $184.77   $184.75   $184.80  
  Purchase #3 $42.44   3.683%   $44.0031   $44.00   $44.00   $44.00  
  Purchase #4 $44.79   10.635%   $49.5534   $49.55   $49.55   $49.60  
  Purchase #5 $209.91   5.733%   $221.9441   $221.94   $221.95   $221.90  
  Purchase #6 $183.81   11.362%   $204.6945   $204.69   $204.70   $204.70  
  Purchase #7 $136.95   8.867%   $149.0934   $149.09   $149.10   $149.10  
  7 purchase totals = $941.26       $1,035.3267   $1,035.31   $1,035.30   $1,035.40