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 $92.35   12.134%   $103.5557   $103.56   $103.55   $103.60  
  Purchase #2 $213.95   4.710%   $224.027   $224.03   $224.05   $224.00  
  Purchase #3 $10.70   7.627%   $11.5161   $11.52   $11.50   $11.50  
  Purchase #4 $201.67   4.177%   $210.0938   $210.09   $210.10   $210.10  
  Purchase #5 $213.95   11.252%   $238.0237   $238.02   $238.00   $238.00  
  Purchase #6 $47.47   5.372%   $50.0201   $50.02   $50.00   $50.00  
  Purchase #7 $124.35   4.220%   $129.5976   $129.60   $129.60   $129.60  
  7 purchase totals = $904.44       $966.8340   $966.84   $966.80   $966.80