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 $216.49   11.692%   $241.802   $241.80   $241.80   $241.80  
  Purchase #2 $163.50   6.580%   $174.2583   $174.26   $174.25   $174.30  
  Purchase #3 $245.82   5.514%   $259.3745   $259.37   $259.35   $259.40  
  Purchase #4 $23.70   7.577%   $25.4957   $25.50   $25.50   $25.50  
  Purchase #5 $171.26   6.332%   $182.1042   $182.10   $182.10   $182.10  
  Purchase #6 $65.80   5.786%   $69.6072   $69.61   $69.60   $69.60  
  Purchase #7 $59.95   11.545%   $66.8712   $66.87   $66.85   $66.90  
  7 purchase totals = $946.52       $1,019.5131   $1,019.51   $1,019.45   $1,019.60