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 $249.57   6.591%   $266.0192   $266.02   $266.00   $266.00  
  Purchase #2 $10.31   9.297%   $11.2685   $11.27   $11.25   $11.30  
  Purchase #3 $132.98   10.245%   $146.6038   $146.60   $146.60   $146.60  
  Purchase #4 $186.33   13.740%   $211.9317   $211.93   $211.95   $211.90  
  Purchase #5 $47.53   8.718%   $51.6737   $51.67   $51.65   $51.70  
  Purchase #6 $51.64   13.682%   $58.7054   $58.71   $58.70   $58.70  
  Purchase #7 $212.60   4.364%   $221.8779   $221.88   $221.90   $221.90  
  7 purchase totals = $890.96       $968.0802   $968.08   $968.05   $968.10