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 $163.41   11.199%   $181.7103   $181.71   $181.70   $181.70  
  Purchase #2 $140.76   3.102%   $145.1264   $145.13   $145.15   $145.10  
  Purchase #3 $84.38   3.464%   $87.3029   $87.30   $87.30   $87.30  
  Purchase #4 $189.40   7.250%   $203.1315   $203.13   $203.15   $203.10  
  Purchase #5 $217.91   13.310%   $246.9138   $246.91   $246.90   $246.90  
  Purchase #6 $243.76   11.304%   $271.3146   $271.31   $271.30   $271.30  
  Purchase #7 $194.35   7.399%   $208.73   $208.73   $208.75   $208.70  
  7 purchase totals = $1,233.97       $1,344.2295   $1,344.22   $1,344.25   $1,344.10