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 $68.42   10.130%   $75.3509   $75.35   $75.35   $75.40  
  Purchase #2 $126.62   9.726%   $138.9351   $138.94   $138.95   $138.90  
  Purchase #3 $173.51   8.154%   $187.658   $187.66   $187.65   $187.70  
  Purchase #4 $126.27   10.680%   $139.7556   $139.76   $139.75   $139.80  
  Purchase #5 $81.84   3.694%   $84.8632   $84.86   $84.85   $84.90  
  Purchase #6 $192.52   13.556%   $218.618   $218.62   $218.60   $218.60  
  Purchase #7 $68.44   3.477%   $70.8197   $70.82   $70.80   $70.80  
  7 purchase totals = $837.62       $916.0005   $916.01   $915.95   $916.10