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 $212.63   10.540%   $235.0412   $235.04   $235.05   $235.00  
  Purchase #2 $187.79   10.382%   $207.2864   $207.29   $207.30   $207.30  
  Purchase #3 $38.29   10.410%   $42.276   $42.28   $42.30   $42.30  
  Purchase #4 $77.92   9.477%   $85.3045   $85.30   $85.30   $85.30  
  Purchase #5 $17.73   6.432%   $18.8704   $18.87   $18.85   $18.90  
  Purchase #6 $67.34   8.419%   $73.0094   $73.01   $73.00   $73.00  
  Purchase #7 $202.27   4.768%   $211.9142   $211.91   $211.90   $211.90  
  7 purchase totals = $803.97       $873.7021   $873.70   $873.70   $873.70