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 $129.81   4.727%   $135.9461   $135.95   $135.95   $135.90  
  Purchase #2 $169.89   10.284%   $187.3615   $187.36   $187.35   $187.40  
  Purchase #3 $194.70   4.623%   $203.701   $203.70   $203.70   $203.70  
  Purchase #4 $94.59   4.362%   $98.716   $98.72   $98.70   $98.70  
  Purchase #5 $132.99   3.631%   $137.8189   $137.82   $137.80   $137.80  
  Purchase #6 $241.53   5.527%   $254.8794   $254.88   $254.90   $254.90  
  Purchase #7 $33.61   11.139%   $37.3538   $37.35   $37.35   $37.40  
  7 purchase totals = $997.12       $1,055.7767   $1,055.78   $1,055.75   $1,055.80