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 $82.73   3.594%   $85.7033   $85.70   $85.70   $85.70  
  Purchase #2 $147.28   4.356%   $153.6955   $153.70   $153.70   $153.70  
  Purchase #3 $64.62   9.323%   $70.6445   $70.64   $70.65   $70.60  
  Purchase #4 $213.96   13.365%   $242.5558   $242.56   $242.55   $242.60  
  Purchase #5 $20.27   12.527%   $22.8092   $22.81   $22.80   $22.80  
  Purchase #6 $177.97   12.622%   $200.4334   $200.43   $200.45   $200.40  
  Purchase #7 $223.33   11.221%   $248.3899   $248.39   $248.40   $248.40  
  7 purchase totals = $930.16       $1,024.2316   $1,024.23   $1,024.25   $1,024.20