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 $44.44   13.841%   $50.5909   $50.59   $50.60   $50.60  
  Purchase #2 $242.97   5.362%   $255.9981   $256.00   $256.00   $256.00  
  Purchase #3 $159.60   10.721%   $176.7107   $176.71   $176.70   $176.70  
  Purchase #4 $190.94   7.231%   $204.7469   $204.75   $204.75   $204.70  
  Purchase #5 $243.72   13.788%   $277.3241   $277.32   $277.30   $277.30  
  Purchase #6 $97.45   12.373%   $109.5075   $109.51   $109.50   $109.50  
  Purchase #7 $166.48   4.774%   $174.4278   $174.43   $174.45   $174.40  
  7 purchase totals = $1,145.60       $1,249.3060   $1,249.31   $1,249.30   $1,249.20