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 $108.49   4.821%   $113.7203   $113.72   $113.70   $113.70  
  Purchase #2 $156.51   13.857%   $178.1976   $178.20   $178.20   $178.20  
  Purchase #3 $70.42   6.343%   $74.8867   $74.89   $74.90   $74.90  
  Purchase #4 $91.46   6.692%   $97.5805   $97.58   $97.60   $97.60  
  Purchase #5 $238.87   11.710%   $266.8417   $266.84   $266.85   $266.80  
  Purchase #6 $201.50   10.344%   $222.3432   $222.34   $222.35   $222.30  
  Purchase #7 $109.68   12.170%   $123.0281   $123.03   $123.05   $123.00  
  7 purchase totals = $976.93       $1,076.5981   $1,076.60   $1,076.65   $1,076.50