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 $176.58   8.848%   $192.2038   $192.20   $192.20   $192.20  
  Purchase #2 $142.88   4.561%   $149.3968   $149.40   $149.40   $149.40  
  Purchase #3 $225.47   12.742%   $254.1994   $254.20   $254.20   $254.20  
  Purchase #4 $99.75   6.681%   $106.4143   $106.41   $106.40   $106.40  
  Purchase #5 $48.83   12.327%   $54.8493   $54.85   $54.85   $54.80  
  Purchase #6 $246.97   11.153%   $274.5146   $274.51   $274.50   $274.50  
  Purchase #7 $154.97   6.723%   $165.3886   $165.39   $165.40   $165.40  
  7 purchase totals = $1,095.45       $1,196.9668   $1,196.96   $1,196.95   $1,196.90