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 $241.78   13.812%   $275.1747   $275.17   $275.15   $275.20  
  Purchase #2 $164.35   11.810%   $183.7597   $183.76   $183.75   $183.80  
  Purchase #3 $188.92   4.617%   $197.6424   $197.64   $197.65   $197.60  
  Purchase #4 $68.85   7.493%   $74.0089   $74.01   $74.00   $74.00  
  Purchase #5 $183.95   11.753%   $205.5696   $205.57   $205.55   $205.60  
  Purchase #6 $13.54   13.418%   $15.3568   $15.36   $15.35   $15.40  
  Purchase #7 $187.58   9.161%   $204.7642   $204.76   $204.75   $204.80  
  7 purchase totals = $1,048.97       $1,156.2763   $1,156.27   $1,156.20   $1,156.40