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 $241.32   8.182%   $261.0648   $261.06   $261.05   $261.10  
  Purchase #2 $208.80   9.590%   $228.8239   $228.82   $228.80   $228.80  
  Purchase #3 $88.57   6.873%   $94.6574   $94.66   $94.65   $94.70  
  Purchase #4 $97.56   12.230%   $109.4916   $109.49   $109.50   $109.50  
  Purchase #5 $68.80   10.557%   $76.0632   $76.06   $76.05   $76.10  
  Purchase #6 $167.96   9.829%   $184.4688   $184.47   $184.45   $184.50  
  Purchase #7 $250.39   12.485%   $281.6512   $281.65   $281.65   $281.70  
  7 purchase totals = $1,123.40       $1,236.2209   $1,236.21   $1,236.15   $1,236.40