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 $88.42   9.755%   $97.0454   $97.05   $97.05   $97.00  
  Purchase #2 $131.96   8.847%   $143.6345   $143.63   $143.65   $143.60  
  Purchase #3 $186.72   8.426%   $202.453   $202.45   $202.45   $202.50  
  Purchase #4 $69.28   10.245%   $76.3777   $76.38   $76.40   $76.40  
  Purchase #5 $245.32   9.307%   $268.1519   $268.15   $268.15   $268.20  
  Purchase #6 $159.80   9.314%   $174.6838   $174.68   $174.70   $174.70  
  Purchase #7 $103.84   11.752%   $116.0433   $116.04   $116.05   $116.00  
  7 purchase totals = $985.34       $1,078.3896   $1,078.38   $1,078.45   $1,078.40