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 $63.77   7.793%   $68.7396   $68.74   $68.75   $68.70  
  Purchase #2 $223.70   12.793%   $252.3179   $252.32   $252.30   $252.30  
  Purchase #3 $192.75   6.319%   $204.9299   $204.93   $204.95   $204.90  
  Purchase #4 $223.46   11.666%   $249.5288   $249.53   $249.55   $249.50  
  Purchase #5 $178.30   9.696%   $195.588   $195.59   $195.60   $195.60  
  Purchase #6 $232.55   8.177%   $251.5656   $251.57   $251.55   $251.60  
  Purchase #7 $229.37   9.508%   $251.1785   $251.18   $251.20   $251.20  
  7 purchase totals = $1,343.90       $1,473.8483   $1,473.86   $1,473.90   $1,473.80