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 $155.78   12.652%   $175.4893   $175.49   $175.50   $175.50  
  Purchase #2 $244.59   11.600%   $272.9624   $272.96   $272.95   $273.00  
  Purchase #3 $199.36   9.689%   $218.676   $218.68   $218.70   $218.70  
  Purchase #4 $198.65   4.871%   $208.3262   $208.33   $208.35   $208.30  
  Purchase #5 $230.97   11.193%   $256.8225   $256.82   $256.80   $256.80  
  Purchase #6 $174.95   10.510%   $193.3372   $193.34   $193.35   $193.30  
  Purchase #7 $36.97   6.340%   $39.3139   $39.31   $39.30   $39.30  
  7 purchase totals = $1,241.27       $1,364.9275   $1,364.93   $1,364.95   $1,364.90