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 $210.48   6.435%   $224.0244   $224.02   $224.00   $224.00  
  Purchase #2 $36.45   13.479%   $41.3631   $41.36   $41.35   $41.40  
  Purchase #3 $56.32   5.164%   $59.2284   $59.23   $59.25   $59.20  
  Purchase #4 $107.81   9.519%   $118.0724   $118.07   $118.05   $118.10  
  Purchase #5 $69.96   10.593%   $77.3709   $77.37   $77.35   $77.40  
  Purchase #6 $238.46   13.156%   $269.8318   $269.83   $269.85   $269.80  
  Purchase #7 $81.29   3.729%   $84.3213   $84.32   $84.30   $84.30  
  7 purchase totals = $800.77       $874.2123   $874.20   $874.15   $874.20