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 $184.63   9.687%   $202.5151   $202.52   $202.50   $202.50  
  Purchase #2 $57.92   5.856%   $61.3118   $61.31   $61.30   $61.30  
  Purchase #3 $156.56   12.124%   $175.5413   $175.54   $175.55   $175.50  
  Purchase #4 $142.42   5.250%   $149.8971   $149.90   $149.90   $149.90  
  Purchase #5 $118.55   4.841%   $124.289   $124.29   $124.30   $124.30  
  Purchase #6 $127.70   7.874%   $137.7551   $137.76   $137.75   $137.80  
  Purchase #7 $87.85   9.168%   $95.9041   $95.90   $95.90   $95.90  
  7 purchase totals = $875.63       $947.2135   $947.22   $947.20   $947.20