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 $214.94   13.594%   $244.1589   $244.16   $244.15   $244.20  
  Purchase #2 $35.49   8.268%   $38.4243   $38.42   $38.40   $38.40  
  Purchase #3 $56.26   3.654%   $58.3157   $58.32   $58.30   $58.30  
  Purchase #4 $124.42   7.817%   $134.1459   $134.15   $134.15   $134.10  
  Purchase #5 $68.93   7.111%   $73.8316   $73.83   $73.85   $73.80  
  Purchase #6 $54.73   11.379%   $60.9577   $60.96   $60.95   $61.00  
  Purchase #7 $250.52   10.767%   $277.4935   $277.49   $277.50   $277.50  
  7 purchase totals = $805.29       $887.3276   $887.33   $887.30   $887.30