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 $222.75   13.845%   $253.5897   $253.59   $253.60   $253.60  
  Purchase #2 $96.44   9.544%   $105.6442   $105.64   $105.65   $105.60  
  Purchase #3 $177.52   6.217%   $188.5564   $188.56   $188.55   $188.60  
  Purchase #4 $149.51   6.824%   $159.7126   $159.71   $159.70   $159.70  
  Purchase #5 $220.34   10.671%   $243.8525   $243.85   $243.85   $243.90  
  Purchase #6 $100.39   6.843%   $107.2597   $107.26   $107.25   $107.30  
  Purchase #7 $22.89   9.370%   $25.0348   $25.03   $25.05   $25.00  
  7 purchase totals = $989.84       $1,083.6499   $1,083.64   $1,083.65   $1,083.70