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 $229.47   10.373%   $253.2729   $253.27   $253.25   $253.30  
  Purchase #2 $98.74   5.322%   $103.9949   $103.99   $104.00   $104.00  
  Purchase #3 $104.34   6.537%   $111.1607   $111.16   $111.15   $111.20  
  Purchase #4 $169.60   4.298%   $176.8894   $176.89   $176.90   $176.90  
  Purchase #5 $120.85   8.348%   $130.9386   $130.94   $130.95   $130.90  
  Purchase #6 $152.66   9.208%   $166.7169   $166.72   $166.70   $166.70  
  Purchase #7 $159.54   11.431%   $177.777   $177.78   $177.80   $177.80  
  7 purchase totals = $1,035.20       $1,120.7504   $1,120.75   $1,120.75   $1,120.80