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 $239.79   11.327%   $266.951   $266.95   $266.95   $267.00  
  Purchase #2 $184.33   12.128%   $206.6855   $206.69   $206.70   $206.70  
  Purchase #3 $218.55   13.547%   $248.157   $248.16   $248.15   $248.20  
  Purchase #4 $181.67   13.590%   $206.359   $206.36   $206.35   $206.40  
  Purchase #5 $43.57   10.442%   $48.1196   $48.12   $48.10   $48.10  
  Purchase #6 $180.84   13.106%   $204.5409   $204.54   $204.55   $204.50  
  Purchase #7 $199.54   12.694%   $224.8696   $224.87   $224.85   $224.90  
  7 purchase totals = $1,248.29       $1,405.6826   $1,405.69   $1,405.65   $1,405.80