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 $117.65   7.261%   $126.1926   $126.19   $126.20   $126.20  
  Purchase #2 $179.34   12.557%   $201.8597   $201.86   $201.85   $201.90  
  Purchase #3 $56.41   3.669%   $58.4797   $58.48   $58.50   $58.50  
  Purchase #4 $142.89   8.370%   $154.8499   $154.85   $154.85   $154.80  
  Purchase #5 $192.29   6.786%   $205.3388   $205.34   $205.35   $205.30  
  Purchase #6 $31.26   4.792%   $32.758   $32.76   $32.75   $32.80  
  Purchase #7 $192.32   11.837%   $215.0849   $215.08   $215.10   $215.10  
  7 purchase totals = $912.16       $994.5636   $994.56   $994.60   $994.60