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 $53.98   8.842%   $58.7529   $58.75   $58.75   $58.80  
  Purchase #2 $246.67   10.837%   $273.4016   $273.40   $273.40   $273.40  
  Purchase #3 $87.35   9.586%   $95.7234   $95.72   $95.70   $95.70  
  Purchase #4 $93.40   6.437%   $99.4122   $99.41   $99.40   $99.40  
  Purchase #5 $88.64   3.829%   $92.034   $92.03   $92.05   $92.00  
  Purchase #6 $198.61   13.720%   $225.8593   $225.86   $225.85   $225.90  
  Purchase #7 $248.60   12.779%   $280.3686   $280.37   $280.35   $280.40  
  7 purchase totals = $1,017.25       $1,125.5520   $1,125.54   $1,125.50   $1,125.60