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 $153.45   6.603%   $163.5823   $163.58   $163.60   $163.60  
  Purchase #2 $229.84   13.551%   $260.9856   $260.99   $261.00   $261.00  
  Purchase #3 $178.71   4.153%   $186.1318   $186.13   $186.15   $186.10  
  Purchase #4 $137.68   11.802%   $153.929   $153.93   $153.95   $153.90  
  Purchase #5 $206.64   9.636%   $226.5518   $226.55   $226.55   $226.60  
  Purchase #6 $174.46   11.520%   $194.5578   $194.56   $194.55   $194.60  
  Purchase #7 $180.98   5.873%   $191.609   $191.61   $191.60   $191.60  
  7 purchase totals = $1,261.76       $1,377.3473   $1,377.35   $1,377.40   $1,377.40