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 $183.58   9.554%   $201.1192   $201.12   $201.10   $201.10  
  Purchase #2 $101.76   13.825%   $115.8283   $115.83   $115.85   $115.80  
  Purchase #3 $17.55   12.250%   $19.6999   $19.70   $19.70   $19.70  
  Purchase #4 $167.90   9.677%   $184.1477   $184.15   $184.15   $184.10  
  Purchase #5 $236.98   11.138%   $263.3748   $263.37   $263.35   $263.40  
  Purchase #6 $234.73   8.133%   $253.8206   $253.82   $253.80   $253.80  
  Purchase #7 $194.69   5.404%   $205.211   $205.21   $205.20   $205.20  
  7 purchase totals = $1,137.19       $1,243.2015   $1,243.20   $1,243.15   $1,243.10