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 $188.81   6.180%   $200.4785   $200.48   $200.50   $200.50  
  Purchase #2 $55.84   3.835%   $57.9815   $57.98   $58.00   $58.00  
  Purchase #3 $198.38   3.805%   $205.9284   $205.93   $205.95   $205.90  
  Purchase #4 $206.58   4.147%   $215.1469   $215.15   $215.15   $215.10  
  Purchase #5 $194.50   4.814%   $203.8632   $203.86   $203.85   $203.90  
  Purchase #6 $95.86   6.280%   $101.88   $101.88   $101.90   $101.90  
  Purchase #7 $187.84   3.155%   $193.7664   $193.77   $193.75   $193.80  
  7 purchase totals = $1,127.81       $1,179.0449   $1,179.05   $1,179.10   $1,179.10