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 $216.81   10.759%   $240.1366   $240.14   $240.15   $240.10  
  Purchase #2 $161.79   8.614%   $175.7266   $175.73   $175.75   $175.70  
  Purchase #3 $202.26   6.806%   $216.0258   $216.03   $216.05   $216.00  
  Purchase #4 $173.32   4.602%   $181.2962   $181.30   $181.30   $181.30  
  Purchase #5 $178.69   5.190%   $187.964   $187.96   $187.95   $188.00  
  Purchase #6 $124.64   6.319%   $132.516   $132.52   $132.50   $132.50  
  Purchase #7 $61.52   5.753%   $65.0592   $65.06   $65.05   $65.10  
  7 purchase totals = $1,119.03       $1,198.7244   $1,198.74   $1,198.75   $1,198.70