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 $218.71   9.424%   $239.3212   $239.32   $239.30   $239.30  
  Purchase #2 $93.25   12.374%   $104.7888   $104.79   $104.80   $104.80  
  Purchase #3 $12.27   13.351%   $13.9082   $13.91   $13.90   $13.90  
  Purchase #4 $92.59   10.479%   $102.2925   $102.29   $102.30   $102.30  
  Purchase #5 $91.96   5.223%   $96.7631   $96.76   $96.75   $96.80  
  Purchase #6 $147.97   9.353%   $161.8096   $161.81   $161.80   $161.80  
  Purchase #7 $235.33   8.173%   $254.5635   $254.56   $254.55   $254.60  
  7 purchase totals = $892.08       $973.4469   $973.44   $973.40   $973.50