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 $73.92   5.116%   $77.7017   $77.70   $77.70   $77.70  
  Purchase #2 $168.74   9.208%   $184.2776   $184.28   $184.30   $184.30  
  Purchase #3 $241.72   13.793%   $275.0604   $275.06   $275.05   $275.10  
  Purchase #4 $212.96   8.844%   $231.7942   $231.79   $231.80   $231.80  
  Purchase #5 $108.51   6.124%   $115.1552   $115.16   $115.15   $115.20  
  Purchase #6 $21.46   10.667%   $23.7491   $23.75   $23.75   $23.70  
  Purchase #7 $96.45   9.106%   $105.2327   $105.23   $105.25   $105.20  
  7 purchase totals = $923.76       $1,012.9709   $1,012.97   $1,013.00   $1,013.00