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 $184.80   10.689%   $204.5533   $204.55   $204.55   $204.60  
  Purchase #2 $36.76   8.381%   $39.8409   $39.84   $39.85   $39.80  
  Purchase #3 $192.26   5.306%   $202.4613   $202.46   $202.45   $202.50  
  Purchase #4 $182.54   4.192%   $190.1921   $190.19   $190.20   $190.20  
  Purchase #5 $19.63   7.546%   $21.1113   $21.11   $21.10   $21.10  
  Purchase #6 $171.37   12.354%   $192.541   $192.54   $192.55   $192.50  
  Purchase #7 $162.60   7.563%   $174.8974   $174.90   $174.90   $174.90  
  7 purchase totals = $949.96       $1,025.5973   $1,025.59   $1,025.60   $1,025.60