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 $207.96   13.410%   $235.8474   $235.85   $235.85   $235.80  
  Purchase #2 $37.72   3.166%   $38.9142   $38.91   $38.90   $38.90  
  Purchase #3 $206.49   12.722%   $232.7597   $232.76   $232.75   $232.80  
  Purchase #4 $219.54   5.371%   $231.3315   $231.33   $231.35   $231.30  
  Purchase #5 $238.93   6.279%   $253.9324   $253.93   $253.95   $253.90  
  Purchase #6 $122.82   8.776%   $133.5987   $133.60   $133.60   $133.60  
  Purchase #7 $109.33   12.433%   $122.923   $122.92   $122.90   $122.90  
  7 purchase totals = $1,142.79       $1,249.3069   $1,249.30   $1,249.30   $1,249.20