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 $202.29   13.722%   $230.0482   $230.05   $230.05   $230.00  
  Purchase #2 $147.25   8.341%   $159.5321   $159.53   $159.55   $159.50  
  Purchase #3 $113.51   11.609%   $126.6874   $126.69   $126.70   $126.70  
  Purchase #4 $49.47   9.842%   $54.3388   $54.34   $54.35   $54.30  
  Purchase #5 $45.54   12.162%   $51.0786   $51.08   $51.10   $51.10  
  Purchase #6 $194.67   13.483%   $220.9174   $220.92   $220.90   $220.90  
  Purchase #7 $23.27   11.730%   $25.9996   $26.00   $26.00   $26.00  
  7 purchase totals = $776.00       $868.6021   $868.61   $868.65   $868.50