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 $41.69   6.813%   $44.5303   $44.53   $44.55   $44.50  
  Purchase #2 $181.56   9.661%   $199.1005   $199.10   $199.10   $199.10  
  Purchase #3 $67.42   11.102%   $74.905   $74.91   $74.90   $74.90  
  Purchase #4 $102.95   9.525%   $112.756   $112.76   $112.75   $112.80  
  Purchase #5 $126.97   11.567%   $141.6566   $141.66   $141.65   $141.70  
  Purchase #6 $164.83   13.253%   $186.6749   $186.67   $186.65   $186.70  
  Purchase #7 $111.65   13.317%   $126.5184   $126.52   $126.50   $126.50  
  7 purchase totals = $797.07       $886.1417   $886.15   $886.10   $886.20