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 $108.61   8.666%   $118.0221   $118.02   $118.00   $118.00  
  Purchase #2 $198.61   5.332%   $209.1999   $209.20   $209.20   $209.20  
  Purchase #3 $13.73   4.818%   $14.3915   $14.39   $14.40   $14.40  
  Purchase #4 $127.97   6.238%   $135.9528   $135.95   $135.95   $136.00  
  Purchase #5 $211.48   10.791%   $234.3008   $234.30   $234.30   $234.30  
  Purchase #6 $56.70   12.180%   $63.6061   $63.61   $63.60   $63.60  
  Purchase #7 $162.87   4.603%   $170.3669   $170.37   $170.35   $170.40  
  7 purchase totals = $879.97       $945.8401   $945.84   $945.80   $945.90