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 $172.97   12.162%   $194.0066   $194.01   $194.00   $194.00  
  Purchase #2 $178.82   5.661%   $188.943   $188.94   $188.95   $188.90  
  Purchase #3 $168.96   11.104%   $187.7213   $187.72   $187.70   $187.70  
  Purchase #4 $49.48   12.460%   $55.6452   $55.65   $55.65   $55.60  
  Purchase #5 $155.69   10.219%   $171.6   $171.60   $171.60   $171.60  
  Purchase #6 $46.67   12.155%   $52.3427   $52.34   $52.35   $52.30  
  Purchase #7 $100.88   11.834%   $112.8181   $112.82   $112.80   $112.80  
  7 purchase totals = $873.47       $963.0769   $963.08   $963.05   $962.90