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 $229.50   9.523%   $251.3553   $251.36   $251.35   $251.40  
  Purchase #2 $200.77   4.406%   $209.6159   $209.62   $209.60   $209.60  
  Purchase #3 $11.85   13.764%   $13.481   $13.48   $13.50   $13.50  
  Purchase #4 $177.98   3.219%   $183.7092   $183.71   $183.70   $183.70  
  Purchase #5 $134.54   4.449%   $140.5257   $140.53   $140.55   $140.50  
  Purchase #6 $20.89   13.248%   $23.6575   $23.66   $23.65   $23.70  
  Purchase #7 $207.74   4.345%   $216.7663   $216.77   $216.75   $216.80  
  7 purchase totals = $983.27       $1,039.1109   $1,039.13   $1,039.10   $1,039.20