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 $179.60   12.308%   $201.7052   $201.71   $201.70   $201.70  
  Purchase #2 $178.73   9.871%   $196.3724   $196.37   $196.35   $196.40  
  Purchase #3 $54.76   9.527%   $59.977   $59.98   $60.00   $60.00  
  Purchase #4 $34.64   11.140%   $38.4989   $38.50   $38.50   $38.50  
  Purchase #5 $130.86   13.568%   $148.6151   $148.62   $148.60   $148.60  
  Purchase #6 $39.74   13.170%   $44.9738   $44.97   $44.95   $45.00  
  Purchase #7 $188.25   13.614%   $213.8784   $213.88   $213.90   $213.90  
  7 purchase totals = $806.58       $904.0208   $904.03   $904.00   $904.10