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 $47.99   8.412%   $52.0269   $52.03   $52.05   $52.00  
  Purchase #2 $233.25   4.167%   $242.9695   $242.97   $242.95   $243.00  
  Purchase #3 $135.96   13.163%   $153.8564   $153.86   $153.85   $153.90  
  Purchase #4 $24.65   12.320%   $27.6869   $27.69   $27.70   $27.70  
  Purchase #5 $245.77   8.637%   $266.9972   $267.00   $267.00   $267.00  
  Purchase #6 $176.48   13.533%   $200.363   $200.36   $200.35   $200.40  
  Purchase #7 $159.34   5.852%   $168.6646   $168.66   $168.65   $168.70  
  7 purchase totals = $1,023.44       $1,112.5645   $1,112.57   $1,112.55   $1,112.70