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 $78.65   8.469%   $85.3109   $85.31   $85.30   $85.30  
  Purchase #2 $215.63   9.241%   $235.5564   $235.56   $235.55   $235.60  
  Purchase #3 $43.36   12.607%   $48.8264   $48.83   $48.85   $48.80  
  Purchase #4 $227.73   13.439%   $258.3346   $258.33   $258.35   $258.30  
  Purchase #5 $249.26   8.192%   $269.6794   $269.68   $269.70   $269.70  
  Purchase #6 $49.64   9.409%   $54.3106   $54.31   $54.30   $54.30  
  Purchase #7 $189.82   13.310%   $215.085   $215.09   $215.10   $215.10  
  7 purchase totals = $1,054.09       $1,167.1033   $1,167.11   $1,167.15   $1,167.10