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 $194.28   3.824%   $201.7093   $201.71   $201.70   $201.70  
  Purchase #2 $14.69   10.551%   $16.2399   $16.24   $16.25   $16.20  
  Purchase #3 $242.53   13.596%   $275.5044   $275.50   $275.50   $275.50  
  Purchase #4 $193.78   6.136%   $205.6703   $205.67   $205.65   $205.70  
  Purchase #5 $156.54   12.185%   $175.6144   $175.61   $175.60   $175.60  
  Purchase #6 $33.43   12.341%   $37.5556   $37.56   $37.55   $37.60  
  Purchase #7 $236.53   4.662%   $247.557   $247.56   $247.55   $247.60  
  7 purchase totals = $1,071.78       $1,159.8509   $1,159.85   $1,159.80   $1,159.90