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 $246.57   11.628%   $275.2412   $275.24   $275.25   $275.20  
  Purchase #2 $33.89   8.710%   $36.8418   $36.84   $36.85   $36.80  
  Purchase #3 $220.68   7.557%   $237.3568   $237.36   $237.35   $237.40  
  Purchase #4 $26.58   10.686%   $29.4203   $29.42   $29.40   $29.40  
  Purchase #5 $222.38   8.686%   $241.6959   $241.70   $241.70   $241.70  
  Purchase #6 $83.93   6.631%   $89.4954   $89.50   $89.50   $89.50  
  Purchase #7 $235.32   8.816%   $256.0658   $256.07   $256.05   $256.10  
  7 purchase totals = $1,069.35       $1,166.1172   $1,166.13   $1,166.10   $1,166.10