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 $98.59   9.541%   $107.9965   $108.00   $108.00   $108.00  
  Purchase #2 $137.90   4.854%   $144.5937   $144.59   $144.60   $144.60  
  Purchase #3 $40.26   3.496%   $41.6675   $41.67   $41.65   $41.70  
  Purchase #4 $205.81   8.362%   $223.0198   $223.02   $223.00   $223.00  
  Purchase #5 $145.42   3.459%   $150.4501   $150.45   $150.45   $150.50  
  Purchase #6 $182.99   5.762%   $193.5339   $193.53   $193.55   $193.50  
  Purchase #7 $155.67   9.646%   $170.6859   $170.69   $170.70   $170.70  
  7 purchase totals = $966.64       $1,031.9474   $1,031.95   $1,031.95   $1,032.00