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 $76.93   11.777%   $85.99   $85.99   $86.00   $86.00  
  Purchase #2 $244.37   6.185%   $259.4843   $259.48   $259.50   $259.50  
  Purchase #3 $213.96   7.228%   $229.425   $229.43   $229.45   $229.40  
  Purchase #4 $205.81   11.627%   $229.7395   $229.74   $229.75   $229.70  
  Purchase #5 $31.76   6.791%   $33.9168   $33.92   $33.90   $33.90  
  Purchase #6 $238.72   3.602%   $247.3187   $247.32   $247.30   $247.30  
  Purchase #7 $239.57   6.818%   $255.9039   $255.90   $255.90   $255.90  
  7 purchase totals = $1,251.12       $1,341.7782   $1,341.78   $1,341.80   $1,341.70