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 $161.45   6.583%   $172.0783   $172.08   $172.10   $172.10  
  Purchase #2 $131.88   5.549%   $139.198   $139.20   $139.20   $139.20  
  Purchase #3 $206.88   3.521%   $214.1642   $214.16   $214.15   $214.20  
  Purchase #4 $88.69   12.420%   $99.7053   $99.71   $99.70   $99.70  
  Purchase #5 $120.82   6.635%   $128.8364   $128.84   $128.85   $128.80  
  Purchase #6 $176.40   11.783%   $197.1852   $197.19   $197.20   $197.20  
  Purchase #7 $25.72   7.369%   $27.6153   $27.62   $27.60   $27.60  
  7 purchase totals = $911.84       $978.7827   $978.80   $978.80   $978.80