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 $69.73   5.654%   $73.6725   $73.67   $73.65   $73.70  
  Purchase #2 $178.54   6.594%   $190.3129   $190.31   $190.30   $190.30  
  Purchase #3 $184.29   9.242%   $201.3221   $201.32   $201.30   $201.30  
  Purchase #4 $63.27   3.450%   $65.4528   $65.45   $65.45   $65.50  
  Purchase #5 $160.39   7.713%   $172.7609   $172.76   $172.75   $172.80  
  Purchase #6 $23.42   11.157%   $26.033   $26.03   $26.05   $26.00  
  Purchase #7 $236.75   12.723%   $266.8717   $266.87   $266.85   $266.90  
  7 purchase totals = $916.39       $996.4259   $996.41   $996.35   $996.50