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 $63.63   5.743%   $67.2843   $67.28   $67.30   $67.30  
  Purchase #2 $101.75   5.375%   $107.2191   $107.22   $107.20   $107.20  
  Purchase #3 $243.62   8.695%   $264.8028   $264.80   $264.80   $264.80  
  Purchase #4 $171.54   12.318%   $192.6703   $192.67   $192.65   $192.70  
  Purchase #5 $100.99   3.865%   $104.8933   $104.89   $104.90   $104.90  
  Purchase #6 $166.93   7.222%   $178.9857   $178.99   $179.00   $179.00  
  Purchase #7 $118.57   5.688%   $125.3143   $125.31   $125.30   $125.30  
  7 purchase totals = $967.03       $1,041.1698   $1,041.16   $1,041.15   $1,041.20