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 $229.37   6.197%   $243.5841   $243.58   $243.60   $243.60  
  Purchase #2 $158.99   7.348%   $170.6726   $170.67   $170.65   $170.70  
  Purchase #3 $61.93   12.512%   $69.6787   $69.68   $69.70   $69.70  
  Purchase #4 $159.46   3.700%   $165.36   $165.36   $165.35   $165.40  
  Purchase #5 $205.48   4.390%   $214.5006   $214.50   $214.50   $214.50  
  Purchase #6 $53.25   12.492%   $59.902   $59.90   $59.90   $59.90  
  Purchase #7 $220.47   12.337%   $247.6694   $247.67   $247.65   $247.70  
  7 purchase totals = $1,088.95       $1,171.3674   $1,171.36   $1,171.35   $1,171.50