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 $62.86   5.458%   $66.2909   $66.29   $66.30   $66.30  
  Purchase #2 $150.42   11.713%   $168.0387   $168.04   $168.05   $168.00  
  Purchase #3 $16.46   7.417%   $17.6808   $17.68   $17.70   $17.70  
  Purchase #4 $212.51   7.620%   $228.7033   $228.70   $228.70   $228.70  
  Purchase #5 $41.50   10.240%   $45.7496   $45.75   $45.75   $45.70  
  Purchase #6 $197.47   4.435%   $206.2278   $206.23   $206.25   $206.20  
  Purchase #7 $225.96   4.564%   $236.2728   $236.27   $236.25   $236.30  
  7 purchase totals = $907.18       $968.9639   $968.96   $969.00   $968.90