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 $69.44   5.654%   $73.3661   $73.37   $73.35   $73.40  
  Purchase #2 $57.86   6.565%   $61.6585   $61.66   $61.65   $61.70  
  Purchase #3 $155.42   6.696%   $165.8269   $165.83   $165.85   $165.80  
  Purchase #4 $30.53   7.564%   $32.8393   $32.84   $32.85   $32.80  
  Purchase #5 $231.75   6.451%   $246.7002   $246.70   $246.70   $246.70  
  Purchase #6 $52.77   11.330%   $58.7488   $58.75   $58.75   $58.70  
  Purchase #7 $35.84   7.764%   $38.6226   $38.62   $38.60   $38.60  
  7 purchase totals = $633.61       $677.7624   $677.77   $677.75   $677.70