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 $68.53   7.833%   $73.898   $73.90   $73.90   $73.90  
  Purchase #2 $249.43   13.794%   $283.8364   $283.84   $283.85   $283.80  
  Purchase #3 $87.54   12.838%   $98.7784   $98.78   $98.80   $98.80  
  Purchase #4 $95.99   6.631%   $102.3551   $102.36   $102.35   $102.40  
  Purchase #5 $183.84   9.297%   $200.9316   $200.93   $200.95   $200.90  
  Purchase #6 $196.26   8.862%   $213.6526   $213.65   $213.65   $213.70  
  Purchase #7 $20.48   4.396%   $21.3803   $21.38   $21.40   $21.40  
  7 purchase totals = $902.07       $994.8324   $994.84   $994.90   $994.90