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 $205.27   9.304%   $224.3683   $224.37   $224.35   $224.40  
  Purchase #2 $142.27   12.419%   $159.9385   $159.94   $159.95   $159.90  
  Purchase #3 $140.79   12.413%   $158.2663   $158.27   $158.25   $158.30  
  Purchase #4 $176.70   3.169%   $182.2996   $182.30   $182.30   $182.30  
  Purchase #5 $97.45   9.651%   $106.8549   $106.85   $106.85   $106.90  
  Purchase #6 $225.79   8.794%   $245.646   $245.65   $245.65   $245.60  
  Purchase #7 $231.33   11.614%   $258.1967   $258.20   $258.20   $258.20  
  7 purchase totals = $1,219.60       $1,335.5703   $1,335.58   $1,335.55   $1,335.60