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 $85.64   11.204%   $95.2351   $95.24   $95.25   $95.20  
  Purchase #2 $142.76   10.579%   $157.8626   $157.86   $157.85   $157.90  
  Purchase #3 $233.91   7.402%   $251.224   $251.22   $251.20   $251.20  
  Purchase #4 $53.75   9.396%   $58.8004   $58.80   $58.80   $58.80  
  Purchase #5 $171.31   11.720%   $191.3875   $191.39   $191.40   $191.40  
  Purchase #6 $83.44   6.158%   $88.5782   $88.58   $88.60   $88.60  
  Purchase #7 $155.96   13.681%   $177.2969   $177.30   $177.30   $177.30  
  7 purchase totals = $926.77       $1,020.3847   $1,020.39   $1,020.40   $1,020.40