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 $65.94   11.583%   $73.5778   $73.58   $73.60   $73.60  
  Purchase #2 $174.32   13.397%   $197.6737   $197.67   $197.65   $197.70  
  Purchase #3 $52.49   7.512%   $56.433   $56.43   $56.45   $56.40  
  Purchase #4 $165.81   7.324%   $177.9539   $177.95   $177.95   $178.00  
  Purchase #5 $228.28   5.312%   $240.4062   $240.41   $240.40   $240.40  
  Purchase #6 $120.56   11.421%   $134.3292   $134.33   $134.35   $134.30  
  Purchase #7 $128.77   8.520%   $139.7412   $139.74   $139.75   $139.70  
  7 purchase totals = $936.17       $1,020.1150   $1,020.11   $1,020.15   $1,020.10