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 $25.88   12.834%   $29.2014   $29.20   $29.20   $29.20  
  Purchase #2 $232.34   9.407%   $254.1962   $254.20   $254.20   $254.20  
  Purchase #3 $224.30   6.112%   $238.0092   $238.01   $238.00   $238.00  
  Purchase #4 $219.27   12.157%   $245.9267   $245.93   $245.95   $245.90  
  Purchase #5 $38.33   4.713%   $40.1365   $40.14   $40.15   $40.10  
  Purchase #6 $178.88   5.216%   $188.2104   $188.21   $188.20   $188.20  
  Purchase #7 $249.29   8.564%   $270.6392   $270.64   $270.65   $270.60  
  7 purchase totals = $1,168.29       $1,266.3196   $1,266.33   $1,266.35   $1,266.20