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 $206.38   6.409%   $219.6069   $219.61   $219.60   $219.60  
  Purchase #2 $70.46   4.472%   $73.611   $73.61   $73.60   $73.60  
  Purchase #3 $183.52   10.369%   $202.5492   $202.55   $202.55   $202.50  
  Purchase #4 $198.80   12.779%   $224.2047   $224.20   $224.20   $224.20  
  Purchase #5 $96.96   3.784%   $100.629   $100.63   $100.65   $100.60  
  Purchase #6 $106.56   8.147%   $115.2414   $115.24   $115.25   $115.20  
  Purchase #7 $33.72   7.206%   $36.1499   $36.15   $36.15   $36.10  
  7 purchase totals = $896.40       $971.9921   $971.99   $972.00   $971.80