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 $65.90   5.600%   $69.5904   $69.59   $69.60   $69.60  
  Purchase #2 $67.36   12.251%   $75.6123   $75.61   $75.60   $75.60  
  Purchase #3 $101.48   12.107%   $113.7662   $113.77   $113.75   $113.80  
  Purchase #4 $179.26   6.209%   $190.3903   $190.39   $190.40   $190.40  
  Purchase #5 $236.80   5.800%   $250.5344   $250.53   $250.55   $250.50  
  Purchase #6 $188.97   8.209%   $204.4825   $204.48   $204.50   $204.50  
  Purchase #7 $132.60   11.632%   $148.024   $148.02   $148.00   $148.00  
  7 purchase totals = $972.37       $1,052.4001   $1,052.39   $1,052.40   $1,052.40