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 $243.94   7.724%   $262.7819   $262.78   $262.80   $262.80  
  Purchase #2 $165.50   5.650%   $174.8508   $174.85   $174.85   $174.90  
  Purchase #3 $160.59   5.514%   $169.4449   $169.44   $169.45   $169.40  
  Purchase #4 $194.72   3.643%   $201.8136   $201.81   $201.80   $201.80  
  Purchase #5 $102.94   4.320%   $107.387   $107.39   $107.40   $107.40  
  Purchase #6 $249.30   6.540%   $265.6042   $265.60   $265.60   $265.60  
  Purchase #7 $171.91   11.667%   $191.9667   $191.97   $191.95   $192.00  
  7 purchase totals = $1,288.90       $1,373.8491   $1,373.84   $1,373.85   $1,373.90