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 $199.68   11.704%   $223.0505   $223.05   $223.05   $223.10  
  Purchase #2 $69.44   8.558%   $75.3827   $75.38   $75.40   $75.40  
  Purchase #3 $114.37   10.732%   $126.6442   $126.64   $126.65   $126.60  
  Purchase #4 $147.33   4.449%   $153.8847   $153.88   $153.90   $153.90  
  Purchase #5 $133.30   4.874%   $139.797   $139.80   $139.80   $139.80  
  Purchase #6 $202.43   3.615%   $209.7478   $209.75   $209.75   $209.70  
  Purchase #7 $87.93   11.137%   $97.7228   $97.72   $97.70   $97.70  
  7 purchase totals = $954.48       $1,026.2297   $1,026.22   $1,026.25   $1,026.20