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 $42.59   12.786%   $48.0356   $48.04   $48.05   $48.00  
  Purchase #2 $238.28   10.322%   $262.8753   $262.88   $262.90   $262.90  
  Purchase #3 $119.53   7.839%   $128.9   $128.90   $128.90   $128.90  
  Purchase #4 $187.51   4.382%   $195.7267   $195.73   $195.75   $195.70  
  Purchase #5 $183.28   7.480%   $196.9893   $196.99   $197.00   $197.00  
  Purchase #6 $203.85   11.257%   $226.7974   $226.80   $226.80   $226.80  
  Purchase #7 $74.74   5.634%   $78.9509   $78.95   $78.95   $79.00  
  7 purchase totals = $1,049.78       $1,138.2752   $1,138.29   $1,138.35   $1,138.30