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 $106.92   5.604%   $112.9118   $112.91   $112.90   $112.90  
  Purchase #2 $212.94   8.218%   $230.4394   $230.44   $230.45   $230.40  
  Purchase #3 $10.83   5.422%   $11.4172   $11.42   $11.40   $11.40  
  Purchase #4 $204.80   4.396%   $213.803   $213.80   $213.80   $213.80  
  Purchase #5 $172.93   5.756%   $182.8839   $182.88   $182.90   $182.90  
  Purchase #6 $149.29   13.737%   $169.798   $169.80   $169.80   $169.80  
  Purchase #7 $103.56   11.656%   $115.631   $115.63   $115.65   $115.60  
  7 purchase totals = $961.27       $1,036.8843   $1,036.88   $1,036.90   $1,036.80