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 $149.67   8.872%   $162.9487   $162.95   $162.95   $162.90  
  Purchase #2 $74.83   10.651%   $82.8001   $82.80   $82.80   $82.80  
  Purchase #3 $96.59   5.689%   $102.085   $102.09   $102.10   $102.10  
  Purchase #4 $216.86   7.397%   $232.9011   $232.90   $232.90   $232.90  
  Purchase #5 $116.92   5.565%   $123.4266   $123.43   $123.45   $123.40  
  Purchase #6 $141.90   9.800%   $155.8062   $155.81   $155.80   $155.80  
  Purchase #7 $22.35   13.192%   $25.2984   $25.30   $25.30   $25.30  
  7 purchase totals = $819.12       $885.2661   $885.28   $885.30   $885.20