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 $57.80   5.804%   $61.1547   $61.15   $61.15   $61.20  
  Purchase #2 $200.86   8.505%   $217.9431   $217.94   $217.95   $217.90  
  Purchase #3 $208.52   12.600%   $234.7935   $234.79   $234.80   $234.80  
  Purchase #4 $93.89   11.494%   $104.6817   $104.68   $104.70   $104.70  
  Purchase #5 $175.33   8.384%   $190.0297   $190.03   $190.05   $190.00  
  Purchase #6 $169.43   6.609%   $180.6276   $180.63   $180.65   $180.60  
  Purchase #7 $68.83   7.822%   $74.2139   $74.21   $74.20   $74.20  
  7 purchase totals = $974.66       $1,063.4442   $1,063.43   $1,063.50   $1,063.40