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 $232.43   5.715%   $245.7134   $245.71   $245.70   $245.70  
  Purchase #2 $143.29   4.196%   $149.3024   $149.30   $149.30   $149.30  
  Purchase #3 $14.47   4.204%   $15.0783   $15.08   $15.10   $15.10  
  Purchase #4 $204.61   5.665%   $216.2012   $216.20   $216.20   $216.20  
  Purchase #5 $84.56   11.514%   $94.2962   $94.30   $94.30   $94.30  
  Purchase #6 $145.39   13.516%   $165.0409   $165.04   $165.05   $165.00  
  Purchase #7 $69.27   7.492%   $74.4597   $74.46   $74.45   $74.50  
  7 purchase totals = $894.02       $960.0921   $960.09   $960.10   $960.10