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 $226.80   8.474%   $246.019   $246.02   $246.00   $246.00  
  Purchase #2 $101.48   6.118%   $107.6885   $107.69   $107.70   $107.70  
  Purchase #3 $36.94   6.531%   $39.3526   $39.35   $39.35   $39.40  
  Purchase #4 $79.92   12.641%   $90.0227   $90.02   $90.00   $90.00  
  Purchase #5 $156.91   6.439%   $167.0134   $167.01   $167.00   $167.00  
  Purchase #6 $9.59   8.440%   $10.3994   $10.40   $10.40   $10.40  
  Purchase #7 $83.72   13.565%   $95.0766   $95.08   $95.10   $95.10  
  7 purchase totals = $695.36       $755.5722   $755.57   $755.55   $755.60