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 $34.83   4.111%   $36.2619   $36.26   $36.25   $36.30  
  Purchase #2 $108.28   6.826%   $115.6712   $115.67   $115.65   $115.70  
  Purchase #3 $22.70   9.812%   $24.9273   $24.93   $24.95   $24.90  
  Purchase #4 $64.67   10.687%   $71.5813   $71.58   $71.60   $71.60  
  Purchase #5 $202.82   12.810%   $228.8012   $228.80   $228.80   $228.80  
  Purchase #6 $127.35   5.227%   $134.0066   $134.01   $134.00   $134.00  
  Purchase #7 $226.47   7.657%   $243.8108   $243.81   $243.80   $243.80  
  7 purchase totals = $787.12       $855.0603   $855.06   $855.05   $855.10