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 $177.39   10.519%   $196.0497   $196.05   $196.05   $196.00  
  Purchase #2 $98.81   3.735%   $102.5006   $102.50   $102.50   $102.50  
  Purchase #3 $96.86   12.142%   $108.6207   $108.62   $108.60   $108.60  
  Purchase #4 $221.80   7.137%   $237.6299   $237.63   $237.65   $237.60  
  Purchase #5 $90.80   9.760%   $99.6621   $99.66   $99.65   $99.70  
  Purchase #6 $147.92   3.246%   $152.7215   $152.72   $152.70   $152.70  
  Purchase #7 $150.56   8.774%   $163.7701   $163.77   $163.75   $163.80  
  7 purchase totals = $984.14       $1,060.9546   $1,060.95   $1,060.90   $1,060.90