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 $160.47   8.398%   $173.9463   $173.95   $173.95   $173.90  
  Purchase #2 $174.27   4.755%   $182.5565   $182.56   $182.55   $182.60  
  Purchase #3 $94.96   7.331%   $101.9215   $101.92   $101.90   $101.90  
  Purchase #4 $200.51   3.147%   $206.82   $206.82   $206.80   $206.80  
  Purchase #5 $80.93   4.634%   $84.6803   $84.68   $84.70   $84.70  
  Purchase #6 $115.26   8.176%   $124.6837   $124.68   $124.70   $124.70  
  Purchase #7 $170.37   3.191%   $175.8065   $175.81   $175.80   $175.80  
  7 purchase totals = $996.77       $1,050.4148   $1,050.42   $1,050.40   $1,050.40