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 $61.89   5.851%   $65.5112   $65.51   $65.50   $65.50  
  Purchase #2 $192.77   5.119%   $202.6379   $202.64   $202.65   $202.60  
  Purchase #3 $97.49   5.117%   $102.4786   $102.48   $102.50   $102.50  
  Purchase #4 $18.80   6.593%   $20.0395   $20.04   $20.05   $20.00  
  Purchase #5 $204.47   13.583%   $232.2432   $232.24   $232.25   $232.20  
  Purchase #6 $184.97   11.166%   $205.6238   $205.62   $205.60   $205.60  
  Purchase #7 $233.32   9.340%   $255.1121   $255.11   $255.10   $255.10  
  7 purchase totals = $993.71       $1,083.6463   $1,083.64   $1,083.65   $1,083.50