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 $225.86   12.177%   $253.363   $253.36   $253.35   $253.40  
  Purchase #2 $161.41   3.804%   $167.55   $167.55   $167.55   $167.60  
  Purchase #3 $167.78   10.746%   $185.8096   $185.81   $185.80   $185.80  
  Purchase #4 $127.33   9.517%   $139.448   $139.45   $139.45   $139.40  
  Purchase #5 $5.52   8.854%   $6.0087   $6.01   $6.00   $6.00  
  Purchase #6 $55.58   12.647%   $62.6092   $62.61   $62.60   $62.60  
  Purchase #7 $200.66   3.489%   $207.661   $207.66   $207.65   $207.70  
  7 purchase totals = $944.14       $1,022.4495   $1,022.45   $1,022.40   $1,022.50