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 $10.82   4.826%   $11.3422   $11.34   $11.35   $11.30  
  Purchase #2 $231.33   9.628%   $253.6025   $253.60   $253.60   $253.60  
  Purchase #3 $98.54   4.697%   $103.1684   $103.17   $103.15   $103.20  
  Purchase #4 $152.68   9.322%   $166.9128   $166.91   $166.90   $166.90  
  Purchase #5 $182.38   11.680%   $203.682   $203.68   $203.70   $203.70  
  Purchase #6 $205.86   12.691%   $231.9857   $231.99   $232.00   $232.00  
  Purchase #7 $153.83   12.561%   $173.1526   $173.15   $173.15   $173.20  
  7 purchase totals = $1,035.44       $1,143.8462   $1,143.84   $1,143.85   $1,143.90