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 $58.47   8.236%   $63.2856   $63.29   $63.30   $63.30  
  Purchase #2 $163.47   7.705%   $176.0654   $176.07   $176.05   $176.10  
  Purchase #3 $211.27   10.132%   $232.6759   $232.68   $232.70   $232.70  
  Purchase #4 $235.27   6.838%   $251.3578   $251.36   $251.35   $251.40  
  Purchase #5 $185.56   9.784%   $203.7152   $203.72   $203.70   $203.70  
  Purchase #6 $98.36   3.298%   $101.6039   $101.60   $101.60   $101.60  
  Purchase #7 $120.45   10.103%   $132.6191   $132.62   $132.60   $132.60  
  7 purchase totals = $1,072.85       $1,161.3229   $1,161.34   $1,161.30   $1,161.40