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 $58.53   12.171%   $65.6537   $65.65   $65.65   $65.70  
  Purchase #2 $194.66   11.294%   $216.6449   $216.64   $216.65   $216.60  
  Purchase #3 $99.98   4.541%   $104.5201   $104.52   $104.50   $104.50  
  Purchase #4 $55.64   13.586%   $63.1993   $63.20   $63.20   $63.20  
  Purchase #5 $25.41   13.435%   $28.8238   $28.82   $28.80   $28.80  
  Purchase #6 $183.83   5.271%   $193.5197   $193.52   $193.50   $193.50  
  Purchase #7 $210.94   6.726%   $225.1278   $225.13   $225.15   $225.10  
  7 purchase totals = $828.99       $897.4893   $897.48   $897.45   $897.40