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 $168.89   10.816%   $187.1571   $187.16   $187.15   $187.20  
  Purchase #2 $41.29   13.618%   $46.9129   $46.91   $46.90   $46.90  
  Purchase #3 $69.45   7.401%   $74.59   $74.59   $74.60   $74.60  
  Purchase #4 $220.57   5.275%   $232.2051   $232.21   $232.20   $232.20  
  Purchase #5 $118.36   5.292%   $124.6236   $124.62   $124.60   $124.60  
  Purchase #6 $190.56   7.761%   $205.3494   $205.35   $205.35   $205.30  
  Purchase #7 $196.87   4.824%   $206.367   $206.37   $206.35   $206.40  
  7 purchase totals = $1,005.99       $1,077.2051   $1,077.21   $1,077.15   $1,077.20