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 $33.72   13.431%   $38.2489   $38.25   $38.25   $38.20  
  Purchase #2 $217.75   9.301%   $238.0029   $238.00   $238.00   $238.00  
  Purchase #3 $29.97   6.511%   $31.9213   $31.92   $31.90   $31.90  
  Purchase #4 $186.54   4.490%   $194.9156   $194.92   $194.90   $194.90  
  Purchase #5 $59.40   4.859%   $62.2862   $62.29   $62.30   $62.30  
  Purchase #6 $176.54   3.395%   $182.5335   $182.53   $182.55   $182.50  
  Purchase #7 $157.95   3.626%   $163.6773   $163.68   $163.70   $163.70  
  7 purchase totals = $861.87       $911.5857   $911.59   $911.60   $911.50