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 $237.96   7.538%   $255.8974   $255.90   $255.90   $255.90  
  Purchase #2 $174.41   5.818%   $184.5572   $184.56   $184.55   $184.60  
  Purchase #3 $24.55   8.732%   $26.6937   $26.69   $26.70   $26.70  
  Purchase #4 $106.34   12.206%   $119.3199   $119.32   $119.30   $119.30  
  Purchase #5 $107.41   10.506%   $118.6945   $118.69   $118.70   $118.70  
  Purchase #6 $192.69   5.847%   $203.9566   $203.96   $203.95   $204.00  
  Purchase #7 $149.87   11.609%   $167.2684   $167.27   $167.25   $167.30  
  7 purchase totals = $993.23       $1,076.3877   $1,076.39   $1,076.35   $1,076.50