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 $17.61   4.316%   $18.37   $18.37   $18.35   $18.40  
  Purchase #2 $88.93   4.238%   $92.6989   $92.70   $92.70   $92.70  
  Purchase #3 $207.26   10.349%   $228.7093   $228.71   $228.70   $228.70  
  Purchase #4 $151.48   7.672%   $163.1015   $163.10   $163.10   $163.10  
  Purchase #5 $219.83   10.664%   $243.2727   $243.27   $243.25   $243.30  
  Purchase #6 $161.45   5.327%   $170.0504   $170.05   $170.05   $170.10  
  Purchase #7 $157.85   7.653%   $169.9303   $169.93   $169.95   $169.90  
  7 purchase totals = $1,004.41       $1,086.1331   $1,086.13   $1,086.10   $1,086.20