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 $48.83   9.864%   $53.6466   $53.65   $53.65   $53.60  
  Purchase #2 $68.36   12.345%   $76.799   $76.80   $76.80   $76.80  
  Purchase #3 $11.97   7.106%   $12.8206   $12.82   $12.80   $12.80  
  Purchase #4 $168.38   3.795%   $174.77   $174.77   $174.75   $174.80  
  Purchase #5 $204.56   11.234%   $227.5403   $227.54   $227.55   $227.50  
  Purchase #6 $184.85   13.359%   $209.5441   $209.54   $209.55   $209.50  
  Purchase #7 $249.58   8.698%   $271.2885   $271.29   $271.30   $271.30  
  7 purchase totals = $936.53       $1,026.4091   $1,026.41   $1,026.40   $1,026.30