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 $187.25   7.839%   $201.9285   $201.93   $201.95   $201.90  
  Purchase #2 $136.77   10.603%   $151.2717   $151.27   $151.25   $151.30  
  Purchase #3 $110.36   12.825%   $124.5137   $124.51   $124.50   $124.50  
  Purchase #4 $115.52   12.661%   $130.146   $130.15   $130.15   $130.10  
  Purchase #5 $250.67   7.186%   $268.6831   $268.68   $268.70   $268.70  
  Purchase #6 $52.84   5.430%   $55.7092   $55.71   $55.70   $55.70  
  Purchase #7 $170.88   4.772%   $179.0344   $179.03   $179.05   $179.00  
  7 purchase totals = $1,024.29       $1,111.2866   $1,111.28   $1,111.30   $1,111.20