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 $21.29   6.254%   $22.6215   $22.62   $22.60   $22.60  
  Purchase #2 $200.85   8.408%   $217.7375   $217.74   $217.75   $217.70  
  Purchase #3 $96.28   3.432%   $99.5843   $99.58   $99.60   $99.60  
  Purchase #4 $241.53   4.230%   $251.7467   $251.75   $251.75   $251.70  
  Purchase #5 $179.30   8.379%   $194.3235   $194.32   $194.30   $194.30  
  Purchase #6 $115.25   9.155%   $125.8011   $125.80   $125.80   $125.80  
  Purchase #7 $103.57   7.676%   $111.52   $111.52   $111.50   $111.50  
  7 purchase totals = $958.07       $1,023.3346   $1,023.33   $1,023.30   $1,023.20