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 $133.45   11.666%   $149.0183   $149.02   $149.00   $149.00  
  Purchase #2 $127.72   6.414%   $135.912   $135.91   $135.90   $135.90  
  Purchase #3 $69.98   11.391%   $77.9514   $77.95   $77.95   $78.00  
  Purchase #4 $133.49   6.637%   $142.3497   $142.35   $142.35   $142.30  
  Purchase #5 $221.51   5.379%   $233.425   $233.43   $233.45   $233.40  
  Purchase #6 $188.52   5.249%   $198.4154   $198.42   $198.40   $198.40  
  Purchase #7 $7.97   12.257%   $8.9469   $8.95   $8.95   $8.90  
  7 purchase totals = $882.64       $946.0187   $946.03   $946.00   $945.90