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 $77.93   8.780%   $84.7723   $84.77   $84.75   $84.80  
  Purchase #2 $175.80   12.195%   $197.2388   $197.24   $197.25   $197.20  
  Purchase #3 $231.96   4.191%   $241.6814   $241.68   $241.70   $241.70  
  Purchase #4 $220.49   10.428%   $243.4827   $243.48   $243.50   $243.50  
  Purchase #5 $23.77   9.177%   $25.9514   $25.95   $25.95   $26.00  
  Purchase #6 $173.42   5.695%   $183.2963   $183.30   $183.30   $183.30  
  Purchase #7 $191.72   10.311%   $211.4882   $211.49   $211.50   $211.50  
  7 purchase totals = $1,095.09       $1,187.9111   $1,187.91   $1,187.95   $1,188.00