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 $192.46   5.261%   $202.5853   $202.59   $202.60   $202.60  
  Purchase #2 $24.27   7.637%   $26.1235   $26.12   $26.10   $26.10  
  Purchase #3 $245.58   10.786%   $272.0683   $272.07   $272.05   $272.10  
  Purchase #4 $142.37   12.358%   $159.9641   $159.96   $159.95   $160.00  
  Purchase #5 $68.71   12.301%   $77.162   $77.16   $77.15   $77.20  
  Purchase #6 $153.58   6.801%   $164.025   $164.03   $164.05   $164.00  
  Purchase #7 $108.82   8.413%   $117.975   $117.98   $118.00   $118.00  
  7 purchase totals = $935.79       $1,019.9032   $1,019.91   $1,019.90   $1,020.00