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 $239.92   4.817%   $251.4769   $251.48   $251.50   $251.50  
  Purchase #2 $47.50   4.631%   $49.6997   $49.70   $49.70   $49.70  
  Purchase #3 $116.52   10.569%   $128.835   $128.84   $128.85   $128.80  
  Purchase #4 $247.55   5.843%   $262.0143   $262.01   $262.00   $262.00  
  Purchase #5 $13.75   4.807%   $14.411   $14.41   $14.40   $14.40  
  Purchase #6 $134.87   12.758%   $152.0767   $152.08   $152.10   $152.10  
  Purchase #7 $46.42   5.658%   $49.0464   $49.05   $49.05   $49.00  
  7 purchase totals = $846.53       $907.5600   $907.57   $907.60   $907.50