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 $82.49   6.172%   $87.5813   $87.58   $87.60   $87.60  
  Purchase #2 $212.91   3.146%   $219.6081   $219.61   $219.60   $219.60  
  Purchase #3 $238.90   5.441%   $251.8985   $251.90   $251.90   $251.90  
  Purchase #4 $17.55   8.139%   $18.9784   $18.98   $19.00   $19.00  
  Purchase #5 $59.87   9.854%   $65.7696   $65.77   $65.75   $65.80  
  Purchase #6 $159.62   7.272%   $171.2276   $171.23   $171.25   $171.20  
  Purchase #7 $167.57   10.235%   $184.7208   $184.72   $184.70   $184.70  
  7 purchase totals = $938.91       $999.7843   $999.79   $999.80   $999.80