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 $204.80   11.731%   $228.8251   $228.83   $228.85   $228.80  
  Purchase #2 $237.81   13.463%   $269.8264   $269.83   $269.85   $269.80  
  Purchase #3 $115.29   9.129%   $125.8148   $125.81   $125.80   $125.80  
  Purchase #4 $19.56   4.311%   $20.4032   $20.40   $20.40   $20.40  
  Purchase #5 $61.37   12.393%   $68.9756   $68.98   $69.00   $69.00  
  Purchase #6 $173.82   12.122%   $194.8905   $194.89   $194.90   $194.90  
  Purchase #7 $144.71   11.763%   $161.7322   $161.73   $161.75   $161.70  
  7 purchase totals = $957.36       $1,070.4678   $1,070.47   $1,070.55   $1,070.40