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 $105.67   11.502%   $117.8242   $117.82   $117.80   $117.80  
  Purchase #2 $156.27   7.819%   $168.4888   $168.49   $168.50   $168.50  
  Purchase #3 $68.54   9.551%   $75.0863   $75.09   $75.10   $75.10  
  Purchase #4 $49.41   11.141%   $54.9148   $54.91   $54.90   $54.90  
  Purchase #5 $206.68   3.767%   $214.4656   $214.47   $214.45   $214.50  
  Purchase #6 $204.71   8.540%   $222.1922   $222.19   $222.20   $222.20  
  Purchase #7 $170.86   4.756%   $178.9861   $178.99   $179.00   $179.00  
  7 purchase totals = $962.14       $1,031.9580   $1,031.96   $1,031.95   $1,032.00