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 $223.32   10.814%   $247.4698   $247.47   $247.45   $247.50  
  Purchase #2 $158.75   13.808%   $180.6702   $180.67   $180.65   $180.70  
  Purchase #3 $74.28   11.224%   $82.6172   $82.62   $82.60   $82.60  
  Purchase #4 $70.95   6.653%   $75.6703   $75.67   $75.65   $75.70  
  Purchase #5 $137.92   3.359%   $142.5527   $142.55   $142.55   $142.60  
  Purchase #6 $204.33   13.654%   $232.2292   $232.23   $232.25   $232.20  
  Purchase #7 $11.65   13.702%   $13.2463   $13.25   $13.25   $13.20  
  7 purchase totals = $881.20       $974.4557   $974.46   $974.40   $974.50