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 $186.88   9.642%   $204.899   $204.90   $204.90   $204.90  
  Purchase #2 $127.82   5.224%   $134.4973   $134.50   $134.50   $134.50  
  Purchase #3 $96.61   12.268%   $108.4621   $108.46   $108.45   $108.50  
  Purchase #4 $120.29   10.472%   $132.8868   $132.89   $132.90   $132.90  
  Purchase #5 $239.25   3.603%   $247.8702   $247.87   $247.85   $247.90  
  Purchase #6 $39.51   10.457%   $43.6416   $43.64   $43.65   $43.60  
  Purchase #7 $71.51   4.444%   $74.6879   $74.69   $74.70   $74.70  
  7 purchase totals = $881.87       $946.9449   $946.95   $946.95   $947.00