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 $88.78   7.846%   $95.7457   $95.75   $95.75   $95.70  
  Purchase #2 $235.33   13.539%   $267.1913   $267.19   $267.20   $267.20  
  Purchase #3 $113.82   13.553%   $129.246   $129.25   $129.25   $129.20  
  Purchase #4 $69.79   3.239%   $72.0505   $72.05   $72.05   $72.10  
  Purchase #5 $82.88   13.490%   $94.0605   $94.06   $94.05   $94.10  
  Purchase #6 $115.72   13.431%   $131.2624   $131.26   $131.25   $131.30  
  Purchase #7 $172.43   8.581%   $187.2262   $187.23   $187.25   $187.20  
  7 purchase totals = $878.75       $976.7826   $976.79   $976.80   $976.80