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 $86.36   8.368%   $93.5866   $93.59   $93.60   $93.60  
  Purchase #2 $33.88   6.216%   $35.986   $35.99   $36.00   $36.00  
  Purchase #3 $175.88   6.807%   $187.8522   $187.85   $187.85   $187.90  
  Purchase #4 $233.44   11.168%   $259.5106   $259.51   $259.50   $259.50  
  Purchase #5 $202.39   4.688%   $211.878   $211.88   $211.90   $211.90  
  Purchase #6 $215.37   9.352%   $235.5114   $235.51   $235.50   $235.50  
  Purchase #7 $12.44   13.313%   $14.0961   $14.10   $14.10   $14.10  
  7 purchase totals = $959.76       $1,038.4209   $1,038.43   $1,038.45   $1,038.50