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 $111.96   6.234%   $118.9396   $118.94   $118.95   $118.90  
  Purchase #2 $65.68   5.421%   $69.2405   $69.24   $69.25   $69.20  
  Purchase #3 $75.36   13.519%   $85.5479   $85.55   $85.55   $85.50  
  Purchase #4 $156.92   6.380%   $166.9315   $166.93   $166.95   $166.90  
  Purchase #5 $116.26   12.386%   $130.66   $130.66   $130.65   $130.70  
  Purchase #6 $227.69   10.258%   $251.0464   $251.05   $251.05   $251.00  
  Purchase #7 $58.99   6.760%   $62.9777   $62.98   $63.00   $63.00  
  7 purchase totals = $812.86       $885.3436   $885.35   $885.40   $885.20