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 $234.83   11.668%   $262.23   $262.23   $262.25   $262.20  
  Purchase #2 $98.50   12.336%   $110.651   $110.65   $110.65   $110.70  
  Purchase #3 $39.66   11.165%   $44.088   $44.09   $44.10   $44.10  
  Purchase #4 $83.65   4.224%   $87.1834   $87.18   $87.20   $87.20  
  Purchase #5 $151.66   10.640%   $167.7966   $167.80   $167.80   $167.80  
  Purchase #6 $14.56   3.409%   $15.0564   $15.06   $15.05   $15.10  
  Purchase #7 $168.63   4.424%   $176.0902   $176.09   $176.10   $176.10  
  7 purchase totals = $791.49       $863.0956   $863.10   $863.15   $863.20