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 $50.64   5.730%   $53.5417   $53.54   $53.55   $53.50  
  Purchase #2 $186.36   4.819%   $195.3407   $195.34   $195.35   $195.30  
  Purchase #3 $165.75   4.743%   $173.6115   $173.61   $173.60   $173.60  
  Purchase #4 $39.49   8.524%   $42.8561   $42.86   $42.85   $42.90  
  Purchase #5 $185.27   10.469%   $204.6659   $204.67   $204.65   $204.70  
  Purchase #6 $112.29   5.750%   $118.7467   $118.75   $118.75   $118.70  
  Purchase #7 $202.76   10.774%   $224.6054   $224.61   $224.60   $224.60  
  7 purchase totals = $942.56       $1,013.3680   $1,013.38   $1,013.35   $1,013.30