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 $108.42   12.322%   $121.7795   $121.78   $121.80   $121.80  
  Purchase #2 $214.75   12.525%   $241.6474   $241.65   $241.65   $241.60  
  Purchase #3 $17.37   5.357%   $18.3005   $18.30   $18.30   $18.30  
  Purchase #4 $134.31   3.221%   $138.6361   $138.64   $138.65   $138.60  
  Purchase #5 $210.61   9.677%   $230.9907   $230.99   $231.00   $231.00  
  Purchase #6 $198.44   4.134%   $206.6435   $206.64   $206.65   $206.60  
  Purchase #7 $64.78   4.468%   $67.6744   $67.67   $67.65   $67.70  
  7 purchase totals = $948.68       $1,025.6721   $1,025.67   $1,025.70   $1,025.60