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 $67.36   8.332%   $72.9724   $72.97   $72.95   $73.00  
  Purchase #2 $179.97   12.399%   $202.2845   $202.28   $202.30   $202.30  
  Purchase #3 $31.70   10.399%   $34.9965   $35.00   $35.00   $35.00  
  Purchase #4 $199.66   8.279%   $216.1899   $216.19   $216.20   $216.20  
  Purchase #5 $113.52   3.426%   $117.4092   $117.41   $117.40   $117.40  
  Purchase #6 $122.80   13.345%   $139.1877   $139.19   $139.20   $139.20  
  Purchase #7 $56.87   12.689%   $64.0862   $64.09   $64.10   $64.10  
  7 purchase totals = $771.88       $847.1264   $847.13   $847.15   $847.20