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 $102.43   9.590%   $112.253   $112.25   $112.25   $112.30  
  Purchase #2 $181.85   7.378%   $195.2669   $195.27   $195.25   $195.30  
  Purchase #3 $16.44   6.864%   $17.5684   $17.57   $17.55   $17.60  
  Purchase #4 $100.66   12.871%   $113.6159   $113.62   $113.60   $113.60  
  Purchase #5 $238.63   10.343%   $263.3115   $263.31   $263.30   $263.30  
  Purchase #6 $126.67   10.124%   $139.4941   $139.49   $139.50   $139.50  
  Purchase #7 $81.53   7.408%   $87.5697   $87.57   $87.55   $87.60  
  7 purchase totals = $848.21       $929.0795   $929.08   $929.00   $929.20