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 $51.52   9.552%   $56.4412   $56.44   $56.45   $56.40  
  Purchase #2 $206.85   13.146%   $234.0425   $234.04   $234.05   $234.00  
  Purchase #3 $240.85   9.287%   $263.2177   $263.22   $263.20   $263.20  
  Purchase #4 $24.72   4.563%   $25.848   $25.85   $25.85   $25.80  
  Purchase #5 $128.50   5.437%   $135.4865   $135.49   $135.50   $135.50  
  Purchase #6 $98.68   6.357%   $104.9531   $104.95   $104.95   $105.00  
  Purchase #7 $13.84   5.137%   $14.551   $14.55   $14.55   $14.60  
  7 purchase totals = $764.96       $834.5400   $834.54   $834.55   $834.50