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 $86.64   12.438%   $97.4163   $97.42   $97.40   $97.40  
  Purchase #2 $192.38   11.414%   $214.3383   $214.34   $214.35   $214.30  
  Purchase #3 $52.99   12.277%   $59.4956   $59.50   $59.50   $59.50  
  Purchase #4 $180.37   11.842%   $201.7294   $201.73   $201.75   $201.70  
  Purchase #5 $240.41   9.814%   $264.0038   $264.00   $264.00   $264.00  
  Purchase #6 $96.46   9.519%   $105.642   $105.64   $105.65   $105.60  
  Purchase #7 $13.51   3.866%   $14.0323   $14.03   $14.05   $14.00  
  7 purchase totals = $862.76       $956.6577   $956.66   $956.70   $956.50