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 $76.67   12.734%   $86.4332   $86.43   $86.45   $86.40  
  Purchase #2 $223.71   5.319%   $235.6091   $235.61   $235.60   $235.60  
  Purchase #3 $146.81   12.347%   $164.9366   $164.94   $164.95   $164.90  
  Purchase #4 $242.82   13.594%   $275.829   $275.83   $275.85   $275.80  
  Purchase #5 $207.66   9.452%   $227.288   $227.29   $227.30   $227.30  
  Purchase #6 $130.49   12.391%   $146.659   $146.66   $146.65   $146.70  
  Purchase #7 $36.50   8.120%   $39.4638   $39.46   $39.45   $39.50  
  7 purchase totals = $1,064.66       $1,176.2187   $1,176.22   $1,176.25   $1,176.20