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 $233.89   5.742%   $247.32   $247.32   $247.30   $247.30  
  Purchase #2 $66.47   8.751%   $72.2868   $72.29   $72.30   $72.30  
  Purchase #3 $153.91   7.326%   $165.1854   $165.19   $165.20   $165.20  
  Purchase #4 $239.32   5.426%   $252.3055   $252.31   $252.30   $252.30  
  Purchase #5 $56.35   12.107%   $63.1723   $63.17   $63.15   $63.20  
  Purchase #6 $6.45   13.614%   $7.3281   $7.33   $7.35   $7.30  
  Purchase #7 $22.44   9.842%   $24.6485   $24.65   $24.65   $24.60  
  7 purchase totals = $778.83       $832.2466   $832.26   $832.25   $832.20