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 $69.54   8.396%   $75.3786   $75.38   $75.40   $75.40  
  Purchase #2 $23.27   5.800%   $24.6197   $24.62   $24.60   $24.60  
  Purchase #3 $53.28   12.679%   $60.0354   $60.04   $60.05   $60.00  
  Purchase #4 $195.70   5.825%   $207.0995   $207.10   $207.10   $207.10  
  Purchase #5 $84.98   10.372%   $93.7941   $93.79   $93.80   $93.80  
  Purchase #6 $94.44   6.151%   $100.249   $100.25   $100.25   $100.20  
  Purchase #7 $134.91   6.848%   $144.1486   $144.15   $144.15   $144.10  
  7 purchase totals = $656.12       $705.3249   $705.33   $705.35   $705.20