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 $205.49   13.672%   $233.5846   $233.58   $233.60   $233.60  
  Purchase #2 $112.66   8.704%   $122.4659   $122.47   $122.45   $122.50  
  Purchase #3 $234.67   5.284%   $247.07   $247.07   $247.05   $247.10  
  Purchase #4 $236.91   12.240%   $265.9078   $265.91   $265.90   $265.90  
  Purchase #5 $160.25   4.564%   $167.5638   $167.56   $167.55   $167.60  
  Purchase #6 $175.65   11.431%   $195.7286   $195.73   $195.75   $195.70  
  Purchase #7 $112.82   4.828%   $118.2669   $118.27   $118.25   $118.30  
  7 purchase totals = $1,238.45       $1,350.5876   $1,350.59   $1,350.55   $1,350.70