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 $208.43   12.343%   $234.1565   $234.16   $234.15   $234.20  
  Purchase #2 $5.61   12.275%   $6.2986   $6.30   $6.30   $6.30  
  Purchase #3 $95.32   7.516%   $102.4843   $102.48   $102.50   $102.50  
  Purchase #4 $183.67   11.119%   $204.0923   $204.09   $204.10   $204.10  
  Purchase #5 $220.83   6.168%   $234.4508   $234.45   $234.45   $234.50  
  Purchase #6 $246.73   3.127%   $254.4452   $254.45   $254.45   $254.40  
  Purchase #7 $83.57   9.378%   $91.4072   $91.41   $91.40   $91.40  
  7 purchase totals = $1,044.16       $1,127.3349   $1,127.34   $1,127.35   $1,127.40