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 $203.57   11.281%   $226.5347   $226.53   $226.55   $226.50  
  Purchase #2 $249.34   5.603%   $263.3105   $263.31   $263.30   $263.30  
  Purchase #3 $124.90   6.194%   $132.6363   $132.64   $132.65   $132.60  
  Purchase #4 $148.98   6.360%   $158.4551   $158.46   $158.45   $158.50  
  Purchase #5 $194.67   9.427%   $213.0215   $213.02   $213.00   $213.00  
  Purchase #6 $177.59   12.256%   $199.3554   $199.36   $199.35   $199.40  
  Purchase #7 $8.40   5.232%   $8.8395   $8.84   $8.85   $8.80  
  7 purchase totals = $1,107.45       $1,202.1530   $1,202.16   $1,202.15   $1,202.10