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 $245.74   11.364%   $273.6659   $273.67   $273.65   $273.70  
  Purchase #2 $54.68   10.408%   $60.3711   $60.37   $60.35   $60.40  
  Purchase #3 $181.26   9.864%   $199.1395   $199.14   $199.15   $199.10  
  Purchase #4 $142.72   11.713%   $159.4368   $159.44   $159.45   $159.40  
  Purchase #5 $118.91   6.527%   $126.6713   $126.67   $126.65   $126.70  
  Purchase #6 $233.63   5.624%   $246.7694   $246.77   $246.75   $246.80  
  Purchase #7 $86.70   9.652%   $95.0683   $95.07   $95.05   $95.10  
  7 purchase totals = $1,063.64       $1,161.1223   $1,161.13   $1,161.05   $1,161.20