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 $202.26   6.799%   $216.0117   $216.01   $216.00   $216.00  
  Purchase #2 $145.37   11.637%   $162.2867   $162.29   $162.30   $162.30  
  Purchase #3 $18.85   5.114%   $19.814   $19.81   $19.80   $19.80  
  Purchase #4 $87.59   3.317%   $90.4954   $90.50   $90.50   $90.50  
  Purchase #5 $217.67   7.218%   $233.3814   $233.38   $233.40   $233.40  
  Purchase #6 $9.28   10.169%   $10.2237   $10.22   $10.20   $10.20  
  Purchase #7 $201.60   3.130%   $207.9101   $207.91   $207.90   $207.90  
  7 purchase totals = $882.62       $940.1230   $940.12   $940.10   $940.10