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 $204.73   12.173%   $229.6518   $229.65   $229.65   $229.70  
  Purchase #2 $189.69   3.659%   $196.6308   $196.63   $196.65   $196.60  
  Purchase #3 $115.77   7.296%   $124.2166   $124.22   $124.20   $124.20  
  Purchase #4 $104.30   10.373%   $115.119   $115.12   $115.10   $115.10  
  Purchase #5 $9.96   11.526%   $11.108   $11.11   $11.10   $11.10  
  Purchase #6 $242.82   13.543%   $275.7051   $275.71   $275.70   $275.70  
  Purchase #7 $185.64   4.873%   $194.6862   $194.69   $194.70   $194.70  
  7 purchase totals = $1,052.91       $1,147.1175   $1,147.13   $1,147.10   $1,147.10