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 $248.96   5.119%   $261.7043   $261.70   $261.70   $261.70  
  Purchase #2 $174.44   13.742%   $198.4115   $198.41   $198.40   $198.40  
  Purchase #3 $200.56   5.530%   $211.651   $211.65   $211.65   $211.70  
  Purchase #4 $244.56   9.629%   $268.1087   $268.11   $268.10   $268.10  
  Purchase #5 $31.25   5.419%   $32.9434   $32.94   $32.95   $32.90  
  Purchase #6 $184.45   3.834%   $191.5218   $191.52   $191.50   $191.50  
  Purchase #7 $250.56   6.601%   $267.0995   $267.10   $267.10   $267.10  
  7 purchase totals = $1,334.78       $1,431.4402   $1,431.43   $1,431.40   $1,431.40