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 $182.33   6.197%   $193.629   $193.63   $193.65   $193.60  
  Purchase #2 $61.59   8.695%   $66.9453   $66.95   $66.95   $66.90  
  Purchase #3 $232.41   9.190%   $253.7685   $253.77   $253.75   $253.80  
  Purchase #4 $100.29   7.204%   $107.5149   $107.51   $107.50   $107.50  
  Purchase #5 $250.78   3.137%   $258.647   $258.65   $258.65   $258.60  
  Purchase #6 $27.43   4.195%   $28.5807   $28.58   $28.60   $28.60  
  Purchase #7 $203.34   10.682%   $225.0608   $225.06   $225.05   $225.10  
  7 purchase totals = $1,058.17       $1,134.1462   $1,134.15   $1,134.15   $1,134.10