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 $89.96   4.743%   $94.2268   $94.23   $94.25   $94.20  
  Purchase #2 $203.73   10.782%   $225.6962   $225.70   $225.70   $225.70  
  Purchase #3 $95.56   12.620%   $107.6197   $107.62   $107.60   $107.60  
  Purchase #4 $110.91   13.121%   $125.4625   $125.46   $125.45   $125.50  
  Purchase #5 $227.87   5.138%   $239.578   $239.58   $239.60   $239.60  
  Purchase #6 $154.51   6.279%   $164.2117   $164.21   $164.20   $164.20  
  Purchase #7 $243.54   10.844%   $269.9495   $269.95   $269.95   $269.90  
  7 purchase totals = $1,126.08       $1,226.7444   $1,226.75   $1,226.75   $1,226.70