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 $60.36   13.413%   $68.4561   $68.46   $68.45   $68.50  
  Purchase #2 $54.56   6.131%   $57.9051   $57.91   $57.90   $57.90  
  Purchase #3 $240.80   5.832%   $254.8435   $254.84   $254.85   $254.80  
  Purchase #4 $76.65   4.495%   $80.0954   $80.10   $80.10   $80.10  
  Purchase #5 $24.51   10.777%   $27.1514   $27.15   $27.15   $27.20  
  Purchase #6 $25.40   5.787%   $26.8699   $26.87   $26.85   $26.90  
  Purchase #7 $246.34   13.360%   $279.251   $279.25   $279.25   $279.30  
  7 purchase totals = $728.62       $794.5724   $794.58   $794.55   $794.70