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 $85.45   8.416%   $92.6415   $92.64   $92.65   $92.60  
  Purchase #2 $113.79   9.109%   $124.1551   $124.16   $124.15   $124.20  
  Purchase #3 $63.65   12.439%   $71.5674   $71.57   $71.55   $71.60  
  Purchase #4 $166.29   3.578%   $172.2399   $172.24   $172.25   $172.20  
  Purchase #5 $146.64   6.384%   $156.0015   $156.00   $156.00   $156.00  
  Purchase #6 $105.28   9.842%   $115.6417   $115.64   $115.65   $115.60  
  Purchase #7 $64.90   6.188%   $68.916   $68.92   $68.90   $68.90  
  7 purchase totals = $746.00       $801.1631   $801.17   $801.15   $801.10