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 $45.71   6.372%   $48.6226   $48.62   $48.60   $48.60  
  Purchase #2 $22.39   4.381%   $23.3709   $23.37   $23.35   $23.40  
  Purchase #3 $181.37   6.317%   $192.8271   $192.83   $192.85   $192.80  
  Purchase #4 $56.93   3.273%   $58.7933   $58.79   $58.80   $58.80  
  Purchase #5 $214.73   12.862%   $242.3486   $242.35   $242.35   $242.30  
  Purchase #6 $158.92   5.786%   $168.1151   $168.12   $168.10   $168.10  
  Purchase #7 $88.98   5.294%   $93.6906   $93.69   $93.70   $93.70  
  7 purchase totals = $769.03       $827.7682   $827.77   $827.75   $827.70