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 $30.37   13.849%   $34.5759   $34.58   $34.60   $34.60  
  Purchase #2 $165.87   10.395%   $183.1122   $183.11   $183.10   $183.10  
  Purchase #3 $219.72   12.642%   $247.497   $247.50   $247.50   $247.50  
  Purchase #4 $205.28   6.362%   $218.3399   $218.34   $218.35   $218.30  
  Purchase #5 $69.77   10.395%   $77.0226   $77.02   $77.00   $77.00  
  Purchase #6 $187.47   11.823%   $209.6346   $209.63   $209.65   $209.60  
  Purchase #7 $54.79   9.522%   $60.0071   $60.01   $60.00   $60.00  
  7 purchase totals = $933.27       $1,030.1893   $1,030.19   $1,030.20   $1,030.10