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 $192.60   5.423%   $203.0447   $203.04   $203.05   $203.00  
  Purchase #2 $88.36   4.210%   $92.08   $92.08   $92.10   $92.10  
  Purchase #3 $88.88   9.690%   $97.4925   $97.49   $97.50   $97.50  
  Purchase #4 $211.81   6.791%   $226.194   $226.19   $226.20   $226.20  
  Purchase #5 $8.80   10.108%   $9.6895   $9.69   $9.70   $9.70  
  Purchase #6 $242.65   7.542%   $260.9507   $260.95   $260.95   $261.00  
  Purchase #7 $108.39   3.780%   $112.4871   $112.49   $112.50   $112.50  
  7 purchase totals = $941.49       $1,001.9385   $1,001.93   $1,002.00   $1,002.00