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 $184.92   12.294%   $207.6541   $207.65   $207.65   $207.70  
  Purchase #2 $24.85   6.188%   $26.3877   $26.39   $26.40   $26.40  
  Purchase #3 $192.33   8.160%   $208.0241   $208.02   $208.00   $208.00  
  Purchase #4 $148.73   7.301%   $159.5888   $159.59   $159.60   $159.60  
  Purchase #5 $85.54   12.516%   $96.2462   $96.25   $96.25   $96.20  
  Purchase #6 $201.31   13.639%   $228.7667   $228.77   $228.75   $228.80  
  Purchase #7 $121.52   12.621%   $136.857   $136.86   $136.85   $136.90  
  7 purchase totals = $959.20       $1,063.5246   $1,063.53   $1,063.50   $1,063.60