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 $57.31   10.574%   $63.37   $63.37   $63.35   $63.40  
  Purchase #2 $194.49   5.414%   $205.0197   $205.02   $205.00   $205.00  
  Purchase #3 $211.91   8.706%   $230.3589   $230.36   $230.35   $230.40  
  Purchase #4 $197.67   8.651%   $214.7704   $214.77   $214.75   $214.80  
  Purchase #5 $129.39   13.271%   $146.5613   $146.56   $146.55   $146.60  
  Purchase #6 $166.85   4.532%   $174.4116   $174.41   $174.40   $174.40  
  Purchase #7 $10.77   9.161%   $11.7566   $11.76   $11.75   $11.80  
  7 purchase totals = $968.39       $1,046.2485   $1,046.25   $1,046.15   $1,046.40