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 $92.59   5.606%   $97.7806   $97.78   $97.80   $97.80  
  Purchase #2 $33.81   6.872%   $36.1334   $36.13   $36.15   $36.10  
  Purchase #3 $207.77   5.327%   $218.8379   $218.84   $218.85   $218.80  
  Purchase #4 $159.86   5.815%   $169.1559   $169.16   $169.15   $169.20  
  Purchase #5 $235.97   3.743%   $244.8024   $244.80   $244.80   $244.80  
  Purchase #6 $157.80   10.843%   $174.9103   $174.91   $174.90   $174.90  
  Purchase #7 $109.50   7.812%   $118.0541   $118.05   $118.05   $118.10  
  7 purchase totals = $997.30       $1,059.6746   $1,059.67   $1,059.70   $1,059.70