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 $92.72   9.212%   $101.2614   $101.26   $101.25   $101.30  
  Purchase #2 $193.92   5.655%   $204.8862   $204.89   $204.90   $204.90  
  Purchase #3 $215.33   5.561%   $227.3045   $227.30   $227.30   $227.30  
  Purchase #4 $77.53   7.697%   $83.4975   $83.50   $83.50   $83.50  
  Purchase #5 $106.54   13.229%   $120.6342   $120.63   $120.65   $120.60  
  Purchase #6 $151.55   10.378%   $167.2779   $167.28   $167.30   $167.30  
  Purchase #7 $246.71   5.322%   $259.8399   $259.84   $259.85   $259.80  
  7 purchase totals = $1,084.30       $1,164.7016   $1,164.70   $1,164.75   $1,164.70