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 $208.74   12.673%   $235.1936   $235.19   $235.20   $235.20  
  Purchase #2 $97.73   11.548%   $109.0159   $109.02   $109.00   $109.00  
  Purchase #3 $103.45   12.636%   $116.5219   $116.52   $116.50   $116.50  
  Purchase #4 $193.62   3.694%   $200.7723   $200.77   $200.75   $200.80  
  Purchase #5 $155.75   4.612%   $162.9332   $162.93   $162.95   $162.90  
  Purchase #6 $55.82   5.614%   $58.9537   $58.95   $58.95   $59.00  
  Purchase #7 $126.49   7.656%   $136.1741   $136.17   $136.15   $136.20  
  7 purchase totals = $941.60       $1,019.5647   $1,019.55   $1,019.50   $1,019.60