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 $175.67   11.497%   $195.8668   $195.87   $195.85   $195.90  
  Purchase #2 $203.69   10.771%   $225.6294   $225.63   $225.65   $225.60  
  Purchase #3 $20.72   7.267%   $22.2257   $22.23   $22.25   $22.20  
  Purchase #4 $240.27   11.535%   $267.9851   $267.99   $268.00   $268.00  
  Purchase #5 $19.44   5.858%   $20.5788   $20.58   $20.60   $20.60  
  Purchase #6 $25.64   4.296%   $26.7415   $26.74   $26.75   $26.70  
  Purchase #7 $165.68   9.578%   $181.5488   $181.55   $181.55   $181.50  
  7 purchase totals = $851.11       $940.5761   $940.59   $940.65   $940.50