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 $167.29   5.663%   $176.7636   $176.76   $176.75   $176.80  
  Purchase #2 $79.75   3.265%   $82.3538   $82.35   $82.35   $82.40  
  Purchase #3 $216.51   5.397%   $228.195   $228.20   $228.20   $228.20  
  Purchase #4 $46.64   10.120%   $51.36   $51.36   $51.35   $51.40  
  Purchase #5 $174.47   7.253%   $187.1243   $187.12   $187.10   $187.10  
  Purchase #6 $184.96   4.330%   $192.9688   $192.97   $192.95   $193.00  
  Purchase #7 $53.95   5.353%   $56.8379   $56.84   $56.85   $56.80  
  7 purchase totals = $923.57       $975.6034   $975.60   $975.55   $975.70