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 $82.99   12.752%   $93.5729   $93.57   $93.55   $93.60  
  Purchase #2 $91.42   5.284%   $96.2506   $96.25   $96.25   $96.30  
  Purchase #3 $224.59   7.213%   $240.7897   $240.79   $240.80   $240.80  
  Purchase #4 $132.42   5.747%   $140.0302   $140.03   $140.05   $140.00  
  Purchase #5 $183.92   11.561%   $205.183   $205.18   $205.20   $205.20  
  Purchase #6 $118.82   12.800%   $134.029   $134.03   $134.05   $134.00  
  Purchase #7 $105.89   6.766%   $113.0545   $113.05   $113.05   $113.10  
  7 purchase totals = $940.05       $1,022.9099   $1,022.90   $1,022.95   $1,023.00