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 $214.39   12.711%   $241.6411   $241.64   $241.65   $241.60  
  Purchase #2 $129.58   11.405%   $144.3586   $144.36   $144.35   $144.40  
  Purchase #3 $209.99   12.153%   $235.5101   $235.51   $235.50   $235.50  
  Purchase #4 $5.44   12.319%   $6.1102   $6.11   $6.10   $6.10  
  Purchase #5 $108.81   4.330%   $113.5215   $113.52   $113.50   $113.50  
  Purchase #6 $239.44   12.648%   $269.7244   $269.72   $269.70   $269.70  
  Purchase #7 $244.84   12.864%   $276.3362   $276.34   $276.35   $276.30  
  7 purchase totals = $1,152.49       $1,287.2021   $1,287.20   $1,287.15   $1,287.10