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 $72.57   13.243%   $82.1804   $82.18   $82.20   $82.20  
  Purchase #2 $98.69   9.426%   $107.9925   $107.99   $108.00   $108.00  
  Purchase #3 $163.59   9.778%   $179.5858   $179.59   $179.60   $179.60  
  Purchase #4 $68.94   7.812%   $74.3256   $74.33   $74.35   $74.30  
  Purchase #5 $131.28   13.113%   $148.4947   $148.49   $148.50   $148.50  
  Purchase #6 $147.96   9.701%   $162.3136   $162.31   $162.30   $162.30  
  Purchase #7 $145.32   11.505%   $162.0391   $162.04   $162.05   $162.00  
  7 purchase totals = $828.35       $916.9317   $916.93   $917.00   $916.90