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 $38.61   12.516%   $43.4424   $43.44   $43.45   $43.40  
  Purchase #2 $165.72   5.151%   $174.2562   $174.26   $174.25   $174.30  
  Purchase #3 $14.57   3.119%   $15.0244   $15.02   $15.00   $15.00  
  Purchase #4 $67.88   12.744%   $76.5306   $76.53   $76.55   $76.50  
  Purchase #5 $140.69   6.129%   $149.3129   $149.31   $149.30   $149.30  
  Purchase #6 $223.74   7.375%   $240.2408   $240.24   $240.25   $240.20  
  Purchase #7 $155.30   3.791%   $161.1874   $161.19   $161.20   $161.20  
  7 purchase totals = $806.51       $859.9947   $859.99   $860.00   $859.90