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 $23.27   13.270%   $26.3579   $26.36   $26.35   $26.40  
  Purchase #2 $192.98   6.628%   $205.7707   $205.77   $205.75   $205.80  
  Purchase #3 $31.33   11.348%   $34.8853   $34.89   $34.90   $34.90  
  Purchase #4 $204.53   4.386%   $213.5007   $213.50   $213.50   $213.50  
  Purchase #5 $196.84   11.210%   $218.9058   $218.91   $218.90   $218.90  
  Purchase #6 $137.98   9.842%   $151.56   $151.56   $151.55   $151.60  
  Purchase #7 $120.49   5.180%   $126.7314   $126.73   $126.75   $126.70  
  7 purchase totals = $907.42       $977.7118   $977.72   $977.70   $977.80