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 $237.89   9.394%   $260.2374   $260.24   $260.25   $260.20  
  Purchase #2 $79.32   8.392%   $85.9765   $85.98   $86.00   $86.00  
  Purchase #3 $234.95   9.618%   $257.5475   $257.55   $257.55   $257.50  
  Purchase #4 $80.52   5.560%   $84.9969   $85.00   $85.00   $85.00  
  Purchase #5 $198.72   6.562%   $211.76   $211.76   $211.75   $211.80  
  Purchase #6 $131.25   11.710%   $146.6194   $146.62   $146.60   $146.60  
  Purchase #7 $206.60   7.490%   $222.0743   $222.07   $222.05   $222.10  
  7 purchase totals = $1,169.25       $1,269.2120   $1,269.22   $1,269.20   $1,269.20