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 $151.75   11.809%   $169.6702   $169.67   $169.65   $169.70  
  Purchase #2 $238.71   10.695%   $264.24   $264.24   $264.25   $264.20  
  Purchase #3 $229.91   10.571%   $254.2138   $254.21   $254.20   $254.20  
  Purchase #4 $96.41   8.527%   $104.6309   $104.63   $104.65   $104.60  
  Purchase #5 $20.93   11.778%   $23.3951   $23.40   $23.40   $23.40  
  Purchase #6 $226.40   8.142%   $244.8335   $244.83   $244.85   $244.80  
  Purchase #7 $179.52   8.250%   $194.3304   $194.33   $194.35   $194.30  
  7 purchase totals = $1,143.63       $1,255.3139   $1,255.31   $1,255.35   $1,255.20