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 $66.64   3.464%   $68.9484   $68.95   $68.95   $68.90  
  Purchase #2 $147.44   13.107%   $166.765   $166.77   $166.75   $166.80  
  Purchase #3 $168.26   4.141%   $175.2276   $175.23   $175.25   $175.20  
  Purchase #4 $56.28   13.330%   $63.7821   $63.78   $63.80   $63.80  
  Purchase #5 $176.44   9.817%   $193.7611   $193.76   $193.75   $193.80  
  Purchase #6 $225.61   9.300%   $246.5917   $246.59   $246.60   $246.60  
  Purchase #7 $120.67   6.201%   $128.1527   $128.15   $128.15   $128.20  
  7 purchase totals = $961.34       $1,043.2286   $1,043.23   $1,043.25   $1,043.30