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 $62.65   11.824%   $70.0577   $70.06   $70.05   $70.10  
  Purchase #2 $123.36   12.548%   $138.8392   $138.84   $138.85   $138.80  
  Purchase #3 $182.84   13.195%   $206.9657   $206.97   $206.95   $207.00  
  Purchase #4 $149.87   3.547%   $155.1859   $155.19   $155.20   $155.20  
  Purchase #5 $178.89   12.614%   $201.4552   $201.46   $201.45   $201.50  
  Purchase #6 $127.70   3.677%   $132.3955   $132.40   $132.40   $132.40  
  Purchase #7 $62.44   13.737%   $71.0174   $71.02   $71.00   $71.00  
  7 purchase totals = $887.75       $975.9166   $975.94   $975.90   $976.00