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 $162.28   12.449%   $182.4822   $182.48   $182.50   $182.50  
  Purchase #2 $244.25   10.278%   $269.354   $269.35   $269.35   $269.40  
  Purchase #3 $35.55   4.868%   $37.2806   $37.28   $37.30   $37.30  
  Purchase #4 $97.55   4.574%   $102.0119   $102.01   $102.00   $102.00  
  Purchase #5 $175.56   13.473%   $199.2132   $199.21   $199.20   $199.20  
  Purchase #6 $83.48   6.226%   $88.6775   $88.68   $88.70   $88.70  
  Purchase #7 $68.94   9.121%   $75.228   $75.23   $75.25   $75.20  
  7 purchase totals = $867.61       $954.2474   $954.24   $954.30   $954.30