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 $174.92   5.686%   $184.866   $184.87   $184.85   $184.90  
  Purchase #2 $35.42   5.475%   $37.3592   $37.36   $37.35   $37.40  
  Purchase #3 $53.87   3.138%   $55.5604   $55.56   $55.55   $55.60  
  Purchase #4 $170.90   9.647%   $187.3867   $187.39   $187.40   $187.40  
  Purchase #5 $157.43   13.231%   $178.2596   $178.26   $178.25   $178.30  
  Purchase #6 $149.29   9.599%   $163.6203   $163.62   $163.60   $163.60  
  Purchase #7 $205.38   8.415%   $222.6627   $222.66   $222.65   $222.70  
  7 purchase totals = $947.21       $1,029.7149   $1,029.72   $1,029.65   $1,029.90