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 $118.55   11.184%   $131.8086   $131.81   $131.80   $131.80  
  Purchase #2 $103.79   9.546%   $113.6978   $113.70   $113.70   $113.70  
  Purchase #3 $93.88   3.154%   $96.841   $96.84   $96.85   $96.80  
  Purchase #4 $34.90   6.476%   $37.1601   $37.16   $37.15   $37.20  
  Purchase #5 $245.42   11.169%   $272.831   $272.83   $272.85   $272.80  
  Purchase #6 $155.35   9.614%   $170.2853   $170.29   $170.30   $170.30  
  Purchase #7 $44.37   12.679%   $49.9957   $50.00   $50.00   $50.00  
  7 purchase totals = $796.26       $872.6195   $872.63   $872.65   $872.60