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 $72.41   6.598%   $77.1876   $77.19   $77.20   $77.20  
  Purchase #2 $218.35   8.411%   $236.7154   $236.72   $236.70   $236.70  
  Purchase #3 $135.64   10.261%   $149.558   $149.56   $149.55   $149.60  
  Purchase #4 $41.45   6.668%   $44.2139   $44.21   $44.20   $44.20  
  Purchase #5 $237.50   4.493%   $248.1709   $248.17   $248.15   $248.20  
  Purchase #6 $221.40   6.579%   $235.9659   $235.97   $235.95   $236.00  
  Purchase #7 $33.78   10.819%   $37.4347   $37.43   $37.45   $37.40  
  7 purchase totals = $960.53       $1,029.2464   $1,029.25   $1,029.20   $1,029.30