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 $70.97   8.394%   $76.9272   $76.93   $76.95   $76.90  
  Purchase #2 $159.79   6.324%   $169.8951   $169.90   $169.90   $169.90  
  Purchase #3 $22.62   5.197%   $23.7956   $23.80   $23.80   $23.80  
  Purchase #4 $138.72   8.686%   $150.7692   $150.77   $150.75   $150.80  
  Purchase #5 $113.39   3.112%   $116.9187   $116.92   $116.90   $116.90  
  Purchase #6 $205.28   9.194%   $224.1534   $224.15   $224.15   $224.20  
  Purchase #7 $220.45   7.747%   $237.5283   $237.53   $237.55   $237.50  
  7 purchase totals = $931.22       $999.9875   $1,000.00   $1,000.00   $1,000.00