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 $164.37   12.486%   $184.8932   $184.89   $184.90   $184.90  
  Purchase #2 $230.29   6.817%   $245.9889   $245.99   $246.00   $246.00  
  Purchase #3 $133.33   3.452%   $137.9326   $137.93   $137.95   $137.90  
  Purchase #4 $169.96   6.645%   $181.2538   $181.25   $181.25   $181.30  
  Purchase #5 $156.97   11.676%   $175.2978   $175.30   $175.30   $175.30  
  Purchase #6 $124.41   5.303%   $131.0075   $131.01   $131.00   $131.00  
  Purchase #7 $65.44   13.766%   $74.4485   $74.45   $74.45   $74.40  
  7 purchase totals = $1,044.77       $1,130.8223   $1,130.82   $1,130.85   $1,130.80