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 $74.59   11.328%   $83.0396   $83.04   $83.05   $83.00  
  Purchase #2 $114.68   4.256%   $119.5608   $119.56   $119.55   $119.60  
  Purchase #3 $116.91   3.524%   $121.0299   $121.03   $121.05   $121.00  
  Purchase #4 $45.88   8.249%   $49.6646   $49.66   $49.65   $49.70  
  Purchase #5 $165.75   9.638%   $181.725   $181.73   $181.75   $181.70  
  Purchase #6 $19.43   13.545%   $22.0618   $22.06   $22.05   $22.10  
  Purchase #7 $201.94   4.294%   $210.6113   $210.61   $210.60   $210.60  
  7 purchase totals = $739.18       $787.6930   $787.69   $787.70   $787.70