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 $224.95   12.472%   $253.0058   $253.01   $253.00   $253.00  
  Purchase #2 $70.44   5.324%   $74.1902   $74.19   $74.20   $74.20  
  Purchase #3 $35.64   3.817%   $37.0004   $37.00   $37.00   $37.00  
  Purchase #4 $167.98   9.593%   $184.0943   $184.09   $184.10   $184.10  
  Purchase #5 $238.70   9.653%   $261.7417   $261.74   $261.75   $261.70  
  Purchase #6 $101.81   13.708%   $115.7661   $115.77   $115.75   $115.80  
  Purchase #7 $155.68   12.103%   $174.522   $174.52   $174.50   $174.50  
  7 purchase totals = $995.20       $1,100.3205   $1,100.32   $1,100.30   $1,100.30