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 $188.46   6.771%   $201.2206   $201.22   $201.20   $201.20  
  Purchase #2 $168.35   13.298%   $190.7372   $190.74   $190.75   $190.70  
  Purchase #3 $230.86   5.201%   $242.867   $242.87   $242.85   $242.90  
  Purchase #4 $126.94   7.488%   $136.4453   $136.45   $136.45   $136.40  
  Purchase #5 $92.52   6.330%   $98.3765   $98.38   $98.40   $98.40  
  Purchase #6 $231.34   9.782%   $253.9697   $253.97   $253.95   $254.00  
  Purchase #7 $59.58   11.195%   $66.25   $66.25   $66.25   $66.30  
  7 purchase totals = $1,098.05       $1,189.8663   $1,189.88   $1,189.85   $1,189.90