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 $191.41   10.562%   $211.6267   $211.63   $211.65   $211.60  
  Purchase #2 $39.27   12.548%   $44.1976   $44.20   $44.20   $44.20  
  Purchase #3 $89.64   4.616%   $93.7778   $93.78   $93.80   $93.80  
  Purchase #4 $119.59   13.141%   $135.3053   $135.31   $135.30   $135.30  
  Purchase #5 $233.63   7.144%   $250.3205   $250.32   $250.30   $250.30  
  Purchase #6 $60.94   6.302%   $64.7804   $64.78   $64.80   $64.80  
  Purchase #7 $30.57   13.195%   $34.6037   $34.60   $34.60   $34.60  
  7 purchase totals = $765.05       $834.6120   $834.62   $834.65   $834.60