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 $182.53   12.723%   $205.7533   $205.75   $205.75   $205.80  
  Purchase #2 $101.29   13.499%   $114.9631   $114.96   $114.95   $115.00  
  Purchase #3 $154.49   13.842%   $175.8745   $175.87   $175.85   $175.90  
  Purchase #4 $17.32   12.199%   $19.4329   $19.43   $19.45   $19.40  
  Purchase #5 $186.65   6.741%   $199.2321   $199.23   $199.25   $199.20  
  Purchase #6 $243.73   11.867%   $272.6534   $272.65   $272.65   $272.70  
  Purchase #7 $205.65   11.232%   $228.7486   $228.75   $228.75   $228.70  
  7 purchase totals = $1,091.66       $1,216.6579   $1,216.64   $1,216.65   $1,216.70