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 $136.63   12.683%   $153.9588   $153.96   $153.95   $154.00  
  Purchase #2 $212.62   10.540%   $235.0301   $235.03   $235.05   $235.00  
  Purchase #3 $188.48   5.508%   $198.8615   $198.86   $198.85   $198.90  
  Purchase #4 $169.87   4.649%   $177.7673   $177.77   $177.75   $177.80  
  Purchase #5 $40.43   12.670%   $45.5525   $45.55   $45.55   $45.60  
  Purchase #6 $117.62   6.718%   $125.5217   $125.52   $125.50   $125.50  
  Purchase #7 $87.87   5.731%   $92.9058   $92.91   $92.90   $92.90  
  7 purchase totals = $953.52       $1,029.5977   $1,029.60   $1,029.55   $1,029.70