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 $134.53   13.460%   $152.6377   $152.64   $152.65   $152.60  
  Purchase #2 $214.36   6.286%   $227.8347   $227.83   $227.85   $227.80  
  Purchase #3 $217.82   11.263%   $242.3531   $242.35   $242.35   $242.40  
  Purchase #4 $189.95   6.170%   $201.6699   $201.67   $201.65   $201.70  
  Purchase #5 $95.99   8.194%   $103.8554   $103.86   $103.85   $103.90  
  Purchase #6 $194.68   10.768%   $215.6431   $215.64   $215.65   $215.60  
  Purchase #7 $81.63   6.592%   $87.011   $87.01   $87.00   $87.00  
  7 purchase totals = $1,128.96       $1,231.0049   $1,231.00   $1,231.00   $1,231.00