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 $63.96   5.827%   $67.6869   $67.69   $67.70   $67.70  
  Purchase #2 $243.54   13.574%   $276.5981   $276.60   $276.60   $276.60  
  Purchase #3 $85.52   3.487%   $88.5021   $88.50   $88.50   $88.50  
  Purchase #4 $200.98   10.206%   $221.492   $221.49   $221.50   $221.50  
  Purchase #5 $12.92   5.585%   $13.6416   $13.64   $13.65   $13.60  
  Purchase #6 $233.57   8.566%   $253.5776   $253.58   $253.60   $253.60  
  Purchase #7 $56.75   8.708%   $61.6918   $61.69   $61.70   $61.70  
  7 purchase totals = $897.24       $983.1901   $983.19   $983.25   $983.20