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 $206.42   11.787%   $230.7507   $230.75   $230.75   $230.80  
  Purchase #2 $119.87   4.842%   $125.6741   $125.67   $125.65   $125.70  
  Purchase #3 $199.90   11.786%   $223.4602   $223.46   $223.45   $223.50  
  Purchase #4 $9.91   4.820%   $10.3877   $10.39   $10.40   $10.40  
  Purchase #5 $231.76   4.321%   $241.7743   $241.77   $241.75   $241.80  
  Purchase #6 $154.67   12.506%   $174.013   $174.01   $174.00   $174.00  
  Purchase #7 $187.83   4.780%   $196.8083   $196.81   $196.80   $196.80  
  7 purchase totals = $1,110.36       $1,202.8683   $1,202.86   $1,202.80   $1,203.00