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 $229.62   10.119%   $252.8552   $252.86   $252.85   $252.90  
  Purchase #2 $125.68   9.276%   $137.3381   $137.34   $137.35   $137.30  
  Purchase #3 $57.28   9.461%   $62.6993   $62.70   $62.70   $62.70  
  Purchase #4 $93.88   4.688%   $98.2811   $98.28   $98.30   $98.30  
  Purchase #5 $232.37   5.140%   $244.3138   $244.31   $244.30   $244.30  
  Purchase #6 $133.40   8.678%   $144.9765   $144.98   $145.00   $145.00  
  Purchase #7 $62.66   8.607%   $68.0531   $68.05   $68.05   $68.10  
  7 purchase totals = $934.89       $1,008.5171   $1,008.52   $1,008.55   $1,008.60