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 $38.33   9.421%   $41.9411   $41.94   $41.95   $41.90  
  Purchase #2 $34.72   13.767%   $39.4999   $39.50   $39.50   $39.50  
  Purchase #3 $40.29   10.477%   $44.5112   $44.51   $44.50   $44.50  
  Purchase #4 $87.92   9.377%   $96.1643   $96.16   $96.15   $96.20  
  Purchase #5 $242.39   10.144%   $266.978   $266.98   $267.00   $267.00  
  Purchase #6 $222.37   13.325%   $252.0008   $252.00   $252.00   $252.00  
  Purchase #7 $135.44   11.432%   $150.9235   $150.92   $150.90   $150.90  
  7 purchase totals = $801.46       $892.0188   $892.01   $892.00   $892.00