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 $235.68   13.551%   $267.617   $267.62   $267.60   $267.60  
  Purchase #2 $206.86   12.482%   $232.6803   $232.68   $232.70   $232.70  
  Purchase #3 $245.96   10.596%   $272.0219   $272.02   $272.00   $272.00  
  Purchase #4 $139.90   8.503%   $151.7957   $151.80   $151.80   $151.80  
  Purchase #5 $219.90   5.799%   $232.652   $232.65   $232.65   $232.70  
  Purchase #6 $57.33   3.231%   $59.1823   $59.18   $59.20   $59.20  
  Purchase #7 $233.37   8.276%   $252.6837   $252.68   $252.70   $252.70  
  7 purchase totals = $1,339.00       $1,468.6329   $1,468.63   $1,468.65   $1,468.70