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 $204.57   4.183%   $213.1272   $213.13   $213.15   $213.10  
  Purchase #2 $31.92   6.563%   $34.0149   $34.01   $34.00   $34.00  
  Purchase #3 $215.29   13.219%   $243.7492   $243.75   $243.75   $243.70  
  Purchase #4 $185.58   12.649%   $209.054   $209.05   $209.05   $209.10  
  Purchase #5 $78.32   9.373%   $85.6609   $85.66   $85.65   $85.70  
  Purchase #6 $240.51   5.573%   $253.9136   $253.91   $253.90   $253.90  
  Purchase #7 $193.78   6.500%   $206.3757   $206.38   $206.40   $206.40  
  7 purchase totals = $1,149.97       $1,245.8955   $1,245.89   $1,245.90   $1,245.90