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 $98.82   10.848%   $109.54   $109.54   $109.55   $109.50  
  Purchase #2 $174.38   9.343%   $190.6723   $190.67   $190.65   $190.70  
  Purchase #3 $212.25   9.569%   $232.5602   $232.56   $232.55   $232.60  
  Purchase #4 $9.89   6.222%   $10.5054   $10.51   $10.50   $10.50  
  Purchase #5 $185.86   5.324%   $195.7552   $195.76   $195.75   $195.80  
  Purchase #6 $178.65   10.447%   $197.3136   $197.31   $197.30   $197.30  
  Purchase #7 $140.91   12.193%   $158.0912   $158.09   $158.10   $158.10  
  7 purchase totals = $1,000.76       $1,094.4379   $1,094.44   $1,094.40   $1,094.50