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 $68.40   13.566%   $77.6791   $77.68   $77.70   $77.70  
  Purchase #2 $62.99   3.160%   $64.9805   $64.98   $65.00   $65.00  
  Purchase #3 $225.46   11.742%   $251.9335   $251.93   $251.95   $251.90  
  Purchase #4 $55.63   10.412%   $61.4222   $61.42   $61.40   $61.40  
  Purchase #5 $83.66   11.540%   $93.3144   $93.31   $93.30   $93.30  
  Purchase #6 $241.39   3.222%   $249.1676   $249.17   $249.15   $249.20  
  Purchase #7 $202.33   6.393%   $215.265   $215.27   $215.25   $215.30  
  7 purchase totals = $939.86       $1,013.7623   $1,013.76   $1,013.75   $1,013.80