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 $86.93   10.792%   $96.3115   $96.31   $96.30   $96.30  
  Purchase #2 $175.81   10.449%   $194.1804   $194.18   $194.20   $194.20  
  Purchase #3 $235.56   3.165%   $243.0155   $243.02   $243.00   $243.00  
  Purchase #4 $32.57   4.773%   $34.1246   $34.12   $34.10   $34.10  
  Purchase #5 $33.59   6.552%   $35.7908   $35.79   $35.80   $35.80  
  Purchase #6 $247.48   10.238%   $272.817   $272.82   $272.80   $272.80  
  Purchase #7 $109.32   5.856%   $115.7218   $115.72   $115.70   $115.70  
  7 purchase totals = $921.26       $991.9616   $991.96   $991.90   $991.90