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 $84.75   9.245%   $92.5851   $92.59   $92.60   $92.60  
  Purchase #2 $184.37   12.269%   $206.9904   $206.99   $207.00   $207.00  
  Purchase #3 $224.37   7.506%   $241.2112   $241.21   $241.20   $241.20  
  Purchase #4 $204.76   3.405%   $211.7321   $211.73   $211.75   $211.70  
  Purchase #5 $105.42   5.356%   $111.0663   $111.07   $111.05   $111.10  
  Purchase #6 $109.88   11.789%   $122.8338   $122.83   $122.85   $122.80  
  Purchase #7 $49.55   10.406%   $54.7062   $54.71   $54.70   $54.70  
  7 purchase totals = $963.10       $1,041.1251   $1,041.13   $1,041.15   $1,041.10