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 $208.62   8.582%   $226.5238   $226.52   $226.50   $226.50  
  Purchase #2 $135.83   10.389%   $149.9414   $149.94   $149.95   $149.90  
  Purchase #3 $110.79   12.314%   $124.4327   $124.43   $124.45   $124.40  
  Purchase #4 $70.41   6.464%   $74.9613   $74.96   $74.95   $75.00  
  Purchase #5 $62.77   13.221%   $71.0688   $71.07   $71.05   $71.10  
  Purchase #6 $113.36   13.349%   $128.4924   $128.49   $128.50   $128.50  
  Purchase #7 $71.37   9.710%   $78.3   $78.30   $78.30   $78.30  
  7 purchase totals = $773.15       $853.7204   $853.71   $853.70   $853.70