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 $208.59   12.792%   $235.2728   $235.27   $235.25   $235.30  
  Purchase #2 $139.99   13.691%   $159.156   $159.16   $159.15   $159.20  
  Purchase #3 $159.69   5.479%   $168.4394   $168.44   $168.45   $168.40  
  Purchase #4 $165.34   10.665%   $182.9735   $182.97   $182.95   $183.00  
  Purchase #5 $185.31   10.483%   $204.736   $204.74   $204.75   $204.70  
  Purchase #6 $215.82   13.560%   $245.0852   $245.09   $245.10   $245.10  
  Purchase #7 $41.81   9.656%   $45.8472   $45.85   $45.85   $45.80  
  7 purchase totals = $1,116.55       $1,241.5101   $1,241.52   $1,241.50   $1,241.50