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 $174.52   4.848%   $182.9807   $182.98   $183.00   $183.00  
  Purchase #2 $93.93   7.139%   $100.6357   $100.64   $100.65   $100.60  
  Purchase #3 $214.75   13.858%   $244.5101   $244.51   $244.50   $244.50  
  Purchase #4 $57.94   13.632%   $65.8384   $65.84   $65.85   $65.80  
  Purchase #5 $122.97   12.721%   $138.613   $138.61   $138.60   $138.60  
  Purchase #6 $250.72   3.169%   $258.6653   $258.67   $258.65   $258.70  
  Purchase #7 $8.66   8.163%   $9.3669   $9.37   $9.35   $9.40  
  7 purchase totals = $923.49       $1,000.6101   $1,000.62   $1,000.60   $1,000.60