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 $60.66   4.106%   $63.1507   $63.15   $63.15   $63.20  
  Purchase #2 $247.26   8.241%   $267.6367   $267.64   $267.65   $267.60  
  Purchase #3 $120.36   8.794%   $130.9445   $130.94   $130.95   $130.90  
  Purchase #4 $190.81   6.436%   $203.0905   $203.09   $203.10   $203.10  
  Purchase #5 $204.65   10.750%   $226.6499   $226.65   $226.65   $226.60  
  Purchase #6 $78.25   12.591%   $88.1025   $88.10   $88.10   $88.10  
  Purchase #7 $101.44   8.516%   $110.0786   $110.08   $110.10   $110.10  
  7 purchase totals = $1,003.43       $1,089.6534   $1,089.65   $1,089.70   $1,089.60