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 $64.82   6.632%   $69.1189   $69.12   $69.10   $69.10  
  Purchase #2 $57.66   11.169%   $64.1   $64.10   $64.10   $64.10  
  Purchase #3 $85.69   11.650%   $95.6729   $95.67   $95.65   $95.70  
  Purchase #4 $64.51   13.222%   $73.0395   $73.04   $73.05   $73.00  
  Purchase #5 $44.60   4.339%   $46.5352   $46.54   $46.55   $46.50  
  Purchase #6 $86.37   11.257%   $96.0927   $96.09   $96.10   $96.10  
  Purchase #7 $175.61   8.193%   $189.9977   $190.00   $190.00   $190.00  
  7 purchase totals = $579.26       $634.5569   $634.56   $634.55   $634.50