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 $67.58   9.256%   $73.8352   $73.84   $73.85   $73.80  
  Purchase #2 $150.59   10.133%   $165.8493   $165.85   $165.85   $165.80  
  Purchase #3 $167.51   11.699%   $187.107   $187.11   $187.10   $187.10  
  Purchase #4 $149.26   4.726%   $156.314   $156.31   $156.30   $156.30  
  Purchase #5 $35.48   10.556%   $39.2253   $39.23   $39.25   $39.20  
  Purchase #6 $163.71   13.861%   $186.4018   $186.40   $186.40   $186.40  
  Purchase #7 $197.45   13.180%   $223.4739   $223.47   $223.45   $223.50  
  7 purchase totals = $931.58       $1,032.2065   $1,032.21   $1,032.20   $1,032.10