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 $54.93   4.831%   $57.5837   $57.58   $57.60   $57.60  
  Purchase #2 $187.33   5.778%   $198.1539   $198.15   $198.15   $198.20  
  Purchase #3 $237.43   9.623%   $260.2779   $260.28   $260.30   $260.30  
  Purchase #4 $158.58   4.703%   $166.038   $166.04   $166.05   $166.00  
  Purchase #5 $43.34   9.532%   $47.4712   $47.47   $47.45   $47.50  
  Purchase #6 $175.58   10.259%   $193.5928   $193.59   $193.60   $193.60  
  Purchase #7 $23.61   5.202%   $24.8382   $24.84   $24.85   $24.80  
  7 purchase totals = $880.80       $947.9557   $947.95   $948.00   $948.00