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 $232.47   3.764%   $241.2202   $241.22   $241.20   $241.20  
  Purchase #2 $94.44   9.810%   $103.7046   $103.70   $103.70   $103.70  
  Purchase #3 $175.88   3.386%   $181.8353   $181.84   $181.85   $181.80  
  Purchase #4 $238.29   4.481%   $248.9678   $248.97   $248.95   $249.00  
  Purchase #5 $80.42   7.439%   $86.4024   $86.40   $86.40   $86.40  
  Purchase #6 $157.74   9.668%   $172.9903   $172.99   $173.00   $173.00  
  Purchase #7 $200.68   8.103%   $216.9411   $216.94   $216.95   $216.90  
  7 purchase totals = $1,179.92       $1,252.0617   $1,252.06   $1,252.05   $1,252.00