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 $50.73   5.112%   $53.3233   $53.32   $53.30   $53.30  
  Purchase #2 $223.49   5.868%   $236.6044   $236.60   $236.60   $236.60  
  Purchase #3 $125.35   3.365%   $129.568   $129.57   $129.55   $129.60  
  Purchase #4 $220.66   13.847%   $251.2148   $251.21   $251.20   $251.20  
  Purchase #5 $128.98   4.365%   $134.61   $134.61   $134.60   $134.60  
  Purchase #6 $33.50   6.760%   $35.7646   $35.76   $35.75   $35.80  
  Purchase #7 $230.68   9.315%   $252.1678   $252.17   $252.15   $252.20  
  7 purchase totals = $1,013.39       $1,093.2529   $1,093.24   $1,093.15   $1,093.30