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 $212.52   6.817%   $227.0075   $227.01   $227.00   $227.00  
  Purchase #2 $109.74   3.565%   $113.6522   $113.65   $113.65   $113.70  
  Purchase #3 $92.54   7.339%   $99.3315   $99.33   $99.35   $99.30  
  Purchase #4 $200.53   3.217%   $206.9811   $206.98   $207.00   $207.00  
  Purchase #5 $61.49   9.769%   $67.497   $67.50   $67.50   $67.50  
  Purchase #6 $131.82   9.761%   $144.687   $144.69   $144.70   $144.70  
  Purchase #7 $12.49   5.409%   $13.1656   $13.17   $13.15   $13.20  
  7 purchase totals = $821.13       $872.3219   $872.33   $872.35   $872.40