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 $52.94   10.726%   $58.6183   $58.62   $58.60   $58.60  
  Purchase #2 $120.48   9.565%   $132.0039   $132.00   $132.00   $132.00  
  Purchase #3 $100.83   3.255%   $104.112   $104.11   $104.10   $104.10  
  Purchase #4 $64.64   4.661%   $67.6529   $67.65   $67.65   $67.70  
  Purchase #5 $93.86   5.764%   $99.2701   $99.27   $99.25   $99.30  
  Purchase #6 $109.98   11.608%   $122.7465   $122.75   $122.75   $122.70  
  Purchase #7 $10.45   9.284%   $11.4202   $11.42   $11.40   $11.40  
  7 purchase totals = $553.18       $595.8239   $595.82   $595.75   $595.80