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 $169.56   9.249%   $185.2426   $185.24   $185.25   $185.20  
  Purchase #2 $63.55   4.165%   $66.1969   $66.20   $66.20   $66.20  
  Purchase #3 $66.52   5.480%   $70.1653   $70.17   $70.15   $70.20  
  Purchase #4 $13.30   12.694%   $14.9883   $14.99   $15.00   $15.00  
  Purchase #5 $120.69   5.716%   $127.5886   $127.59   $127.60   $127.60  
  Purchase #6 $203.55   12.114%   $228.208   $228.21   $228.20   $228.20  
  Purchase #7 $217.44   12.588%   $244.8113   $244.81   $244.80   $244.80  
  7 purchase totals = $854.61       $937.2010   $937.21   $937.20   $937.20