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   13.782%   $68.6788   $68.68   $68.70   $68.70  
  Purchase #2 $69.52   10.521%   $76.8342   $76.83   $76.85   $76.80  
  Purchase #3 $81.60   5.533%   $86.1149   $86.11   $86.10   $86.10  
  Purchase #4 $194.66   6.221%   $206.7698   $206.77   $206.75   $206.80  
  Purchase #5 $116.26   6.765%   $124.125   $124.13   $124.15   $124.10  
  Purchase #6 $54.59   12.413%   $61.3663   $61.37   $61.35   $61.40  
  Purchase #7 $118.44   10.179%   $130.496   $130.50   $130.50   $130.50  
  7 purchase totals = $695.43       $754.3850   $754.39   $754.40   $754.40