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 $169.28   10.787%   $187.5402   $187.54   $187.55   $187.50  
  Purchase #2 $93.58   13.394%   $106.1141   $106.11   $106.10   $106.10  
  Purchase #3 $60.39   7.444%   $64.8854   $64.89   $64.90   $64.90  
  Purchase #4 $68.26   8.292%   $73.9201   $73.92   $73.90   $73.90  
  Purchase #5 $47.64   11.484%   $53.111   $53.11   $53.10   $53.10  
  Purchase #6 $24.77   10.290%   $27.3188   $27.32   $27.30   $27.30  
  Purchase #7 $193.91   13.382%   $219.859   $219.86   $219.85   $219.90  
  7 purchase totals = $657.83       $732.7486   $732.75   $732.70   $732.70