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 $168.93   13.376%   $191.5261   $191.53   $191.55   $191.50  
  Purchase #2 $210.68   10.191%   $232.1504   $232.15   $232.15   $232.20  
  Purchase #3 $246.37   12.665%   $277.5728   $277.57   $277.55   $277.60  
  Purchase #4 $13.59   7.532%   $14.6136   $14.61   $14.60   $14.60  
  Purchase #5 $45.74   5.261%   $48.1464   $48.15   $48.15   $48.10  
  Purchase #6 $92.39   6.805%   $98.6771   $98.68   $98.70   $98.70  
  Purchase #7 $227.98   5.620%   $240.7925   $240.79   $240.80   $240.80  
  7 purchase totals = $1,005.68       $1,103.4789   $1,103.48   $1,103.50   $1,103.50