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 $61.34   8.579%   $66.6024   $66.60   $66.60   $66.60  
  Purchase #2 $145.69   4.103%   $151.6677   $151.67   $151.65   $151.70  
  Purchase #3 $212.86   9.160%   $232.358   $232.36   $232.35   $232.40  
  Purchase #4 $205.81   8.383%   $223.0631   $223.06   $223.05   $223.10  
  Purchase #5 $92.82   6.261%   $98.6315   $98.63   $98.65   $98.60  
  Purchase #6 $220.95   13.159%   $250.0248   $250.02   $250.00   $250.00  
  Purchase #7 $78.97   12.136%   $88.5538   $88.55   $88.55   $88.60  
  7 purchase totals = $1,018.44       $1,110.9013   $1,110.89   $1,110.85   $1,111.00