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 $202.59   4.143%   $210.9833   $210.98   $211.00   $211.00  
  Purchase #2 $151.74   13.522%   $172.2583   $172.26   $172.25   $172.30  
  Purchase #3 $50.51   8.627%   $54.8675   $54.87   $54.85   $54.90  
  Purchase #4 $82.64   5.365%   $87.0736   $87.07   $87.05   $87.10  
  Purchase #5 $189.57   12.802%   $213.8388   $213.84   $213.85   $213.80  
  Purchase #6 $59.51   10.777%   $65.9234   $65.92   $65.90   $65.90  
  Purchase #7 $64.46   5.571%   $68.0511   $68.05   $68.05   $68.10  
  7 purchase totals = $801.02       $872.9960   $872.99   $872.95   $873.10