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 $59.47   7.541%   $63.9546   $63.95   $63.95   $64.00  
  Purchase #2 $168.57   11.367%   $187.7314   $187.73   $187.75   $187.70  
  Purchase #3 $147.28   9.792%   $161.7017   $161.70   $161.70   $161.70  
  Purchase #4 $80.67   6.708%   $86.0813   $86.08   $86.10   $86.10  
  Purchase #5 $104.67   3.161%   $107.9786   $107.98   $108.00   $108.00  
  Purchase #6 $118.70   7.267%   $127.3259   $127.33   $127.35   $127.30  
  Purchase #7 $154.92   10.616%   $171.3663   $171.37   $171.35   $171.40  
  7 purchase totals = $834.28       $906.1398   $906.14   $906.20   $906.20