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 $51.83   6.826%   $55.3679   $55.37   $55.35   $55.40  
  Purchase #2 $167.84   8.231%   $181.6549   $181.65   $181.65   $181.70  
  Purchase #3 $113.50   9.789%   $124.6105   $124.61   $124.60   $124.60  
  Purchase #4 $171.57   10.547%   $189.6655   $189.67   $189.65   $189.70  
  Purchase #5 $153.52   5.106%   $161.3587   $161.36   $161.35   $161.40  
  Purchase #6 $165.80   7.853%   $178.8203   $178.82   $178.80   $178.80  
  Purchase #7 $127.69   3.499%   $132.1579   $132.16   $132.15   $132.20  
  7 purchase totals = $951.75       $1,023.6357   $1,023.64   $1,023.55   $1,023.80