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 $213.69   13.229%   $241.9591   $241.96   $241.95   $242.00  
  Purchase #2 $13.77   11.122%   $15.3015   $15.30   $15.30   $15.30  
  Purchase #3 $136.93   3.679%   $141.9677   $141.97   $141.95   $142.00  
  Purchase #4 $218.80   6.284%   $232.5494   $232.55   $232.55   $232.50  
  Purchase #5 $96.94   13.495%   $110.0221   $110.02   $110.00   $110.00  
  Purchase #6 $201.26   4.725%   $210.7695   $210.77   $210.75   $210.80  
  Purchase #7 $150.95   5.410%   $159.1164   $159.12   $159.10   $159.10  
  7 purchase totals = $1,032.34       $1,111.6857   $1,111.69   $1,111.60   $1,111.70