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 $85.97   12.133%   $96.4007   $96.40   $96.40   $96.40  
  Purchase #2 $175.81   10.217%   $193.7725   $193.77   $193.75   $193.80  
  Purchase #3 $170.29   5.495%   $179.6474   $179.65   $179.65   $179.60  
  Purchase #4 $224.37   4.420%   $234.2872   $234.29   $234.30   $234.30  
  Purchase #5 $181.62   9.295%   $198.5016   $198.50   $198.50   $198.50  
  Purchase #6 $58.96   4.466%   $61.5932   $61.59   $61.60   $61.60  
  Purchase #7 $45.74   6.157%   $48.5562   $48.56   $48.55   $48.60  
  7 purchase totals = $942.76       $1,012.7588   $1,012.76   $1,012.75   $1,012.80