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 $119.89   10.253%   $132.1823   $132.18   $132.20   $132.20  
  Purchase #2 $183.88   11.739%   $205.4657   $205.47   $205.45   $205.50  
  Purchase #3 $202.79   8.224%   $219.4674   $219.47   $219.45   $219.50  
  Purchase #4 $97.55   4.614%   $102.051   $102.05   $102.05   $102.10  
  Purchase #5 $182.43   5.845%   $193.093   $193.09   $193.10   $193.10  
  Purchase #6 $34.57   10.508%   $38.2026   $38.20   $38.20   $38.20  
  Purchase #7 $117.25   7.667%   $126.2396   $126.24   $126.25   $126.20  
  7 purchase totals = $938.36       $1,016.7016   $1,016.70   $1,016.70   $1,016.80