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 $189.83   10.600%   $209.952   $209.95   $209.95   $210.00  
  Purchase #2 $132.36   4.718%   $138.6047   $138.60   $138.60   $138.60  
  Purchase #3 $235.87   6.412%   $250.994   $250.99   $251.00   $251.00  
  Purchase #4 $112.74   13.610%   $128.0839   $128.08   $128.10   $128.10  
  Purchase #5 $61.48   5.559%   $64.8977   $64.90   $64.90   $64.90  
  Purchase #6 $157.28   10.571%   $173.9061   $173.91   $173.90   $173.90  
  Purchase #7 $25.42   9.430%   $27.8171   $27.82   $27.80   $27.80  
  7 purchase totals = $914.98       $994.2555   $994.25   $994.25   $994.30