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 $214.65   8.532%   $232.9639   $232.96   $232.95   $233.00  
  Purchase #2 $219.74   13.168%   $248.6754   $248.68   $248.70   $248.70  
  Purchase #3 $138.58   12.198%   $155.484   $155.48   $155.50   $155.50  
  Purchase #4 $75.69   10.837%   $83.8925   $83.89   $83.90   $83.90  
  Purchase #5 $240.54   6.480%   $256.127   $256.13   $256.15   $256.10  
  Purchase #6 $152.47   8.392%   $165.2653   $165.27   $165.25   $165.30  
  Purchase #7 $161.66   3.186%   $166.8105   $166.81   $166.80   $166.80  
  7 purchase totals = $1,203.33       $1,309.2186   $1,309.22   $1,309.25   $1,309.30