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 $150.65   9.523%   $164.9964   $165.00   $165.00   $165.00  
  Purchase #2 $87.53   7.548%   $94.1368   $94.14   $94.15   $94.10  
  Purchase #3 $24.76   5.190%   $26.045   $26.05   $26.05   $26.00  
  Purchase #4 $115.97   13.414%   $131.5262   $131.53   $131.55   $131.50  
  Purchase #5 $233.78   12.629%   $263.3041   $263.30   $263.30   $263.30  
  Purchase #6 $163.70   4.521%   $171.1009   $171.10   $171.10   $171.10  
  Purchase #7 $245.50   9.432%   $268.6556   $268.66   $268.65   $268.70  
  7 purchase totals = $1,021.89       $1,119.7650   $1,119.78   $1,119.80   $1,119.70