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 $61.30   13.700%   $69.6981   $69.70   $69.70   $69.70  
  Purchase #2 $245.79   5.229%   $258.6424   $258.64   $258.65   $258.60  
  Purchase #3 $202.38   7.714%   $217.9916   $217.99   $218.00   $218.00  
  Purchase #4 $101.66   6.109%   $107.8704   $107.87   $107.85   $107.90  
  Purchase #5 $249.44   3.769%   $258.8414   $258.84   $258.85   $258.80  
  Purchase #6 $120.87   7.814%   $130.3148   $130.31   $130.30   $130.30  
  Purchase #7 $16.36   12.477%   $18.4012   $18.40   $18.40   $18.40  
  7 purchase totals = $997.80       $1,061.7599   $1,061.75   $1,061.75   $1,061.70