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 $53.62   9.257%   $58.5836   $58.58   $58.60   $58.60  
  Purchase #2 $132.55   3.106%   $136.667   $136.67   $136.65   $136.70  
  Purchase #3 $106.83   12.133%   $119.7917   $119.79   $119.80   $119.80  
  Purchase #4 $148.50   3.473%   $153.6574   $153.66   $153.65   $153.70  
  Purchase #5 $182.44   7.546%   $196.2069   $196.21   $196.20   $196.20  
  Purchase #6 $73.30   12.445%   $82.4222   $82.42   $82.40   $82.40  
  Purchase #7 $234.85   8.280%   $254.2956   $254.30   $254.30   $254.30  
  7 purchase totals = $932.09       $1,001.6244   $1,001.63   $1,001.60   $1,001.70