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 $55.41   6.173%   $58.8305   $58.83   $58.85   $58.80  
  Purchase #2 $111.48   8.506%   $120.9625   $120.96   $120.95   $121.00  
  Purchase #3 $125.95   8.558%   $136.7288   $136.73   $136.75   $136.70  
  Purchase #4 $166.29   12.631%   $187.2941   $187.29   $187.30   $187.30  
  Purchase #5 $49.29   5.381%   $51.9423   $51.94   $51.95   $51.90  
  Purchase #6 $247.80   11.220%   $275.6032   $275.60   $275.60   $275.60  
  Purchase #7 $187.41   3.135%   $193.2853   $193.29   $193.30   $193.30  
  7 purchase totals = $943.63       $1,024.6467   $1,024.64   $1,024.70   $1,024.60