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 $195.51   9.316%   $213.7237   $213.72   $213.70   $213.70  
  Purchase #2 $210.29   11.303%   $234.0591   $234.06   $234.05   $234.10  
  Purchase #3 $230.75   6.172%   $244.9919   $244.99   $245.00   $245.00  
  Purchase #4 $46.99   3.287%   $48.5346   $48.53   $48.55   $48.50  
  Purchase #5 $219.49   4.511%   $229.3912   $229.39   $229.40   $229.40  
  Purchase #6 $29.66   4.427%   $30.973   $30.97   $30.95   $31.00  
  Purchase #7 $58.46   10.685%   $64.7065   $64.71   $64.70   $64.70  
  7 purchase totals = $991.15       $1,066.3800   $1,066.37   $1,066.35   $1,066.40