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 $163.99   6.725%   $175.0183   $175.02   $175.00   $175.00  
  Purchase #2 $226.39   11.626%   $252.7101   $252.71   $252.70   $252.70  
  Purchase #3 $50.98   7.221%   $54.6613   $54.66   $54.65   $54.70  
  Purchase #4 $22.34   8.431%   $24.2235   $24.22   $24.20   $24.20  
  Purchase #5 $226.82   3.185%   $234.0442   $234.04   $234.05   $234.00  
  Purchase #6 $38.79   8.248%   $41.9894   $41.99   $42.00   $42.00  
  Purchase #7 $22.96   7.600%   $24.705   $24.71   $24.70   $24.70  
  7 purchase totals = $752.27       $807.3518   $807.35   $807.30   $807.30