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 $42.59   13.152%   $48.1914   $48.19   $48.20   $48.20  
  Purchase #2 $249.74   13.244%   $282.8156   $282.82   $282.80   $282.80  
  Purchase #3 $121.56   11.353%   $135.3607   $135.36   $135.35   $135.40  
  Purchase #4 $25.96   13.663%   $29.5069   $29.51   $29.50   $29.50  
  Purchase #5 $81.36   7.418%   $87.3953   $87.40   $87.40   $87.40  
  Purchase #6 $186.64   11.739%   $208.5497   $208.55   $208.55   $208.50  
  Purchase #7 $229.85   12.317%   $258.1606   $258.16   $258.15   $258.20  
  7 purchase totals = $937.70       $1,049.9802   $1,049.99   $1,049.95   $1,050.00