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 $161.75   13.827%   $184.1152   $184.12   $184.10   $184.10  
  Purchase #2 $221.64   9.784%   $243.3253   $243.33   $243.35   $243.30  
  Purchase #3 $81.37   5.687%   $85.9975   $86.00   $86.00   $86.00  
  Purchase #4 $59.88   3.257%   $61.8303   $61.83   $61.85   $61.80  
  Purchase #5 $173.73   4.589%   $181.7025   $181.70   $181.70   $181.70  
  Purchase #6 $87.90   9.164%   $95.9552   $95.96   $95.95   $96.00  
  Purchase #7 $171.83   11.264%   $191.1849   $191.18   $191.20   $191.20  
  7 purchase totals = $958.10       $1,044.1109   $1,044.12   $1,044.15   $1,044.10