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 $174.57   3.298%   $180.3273   $180.33   $180.35   $180.30  
  Purchase #2 $77.80   4.157%   $81.0341   $81.03   $81.05   $81.00  
  Purchase #3 $27.33   3.825%   $28.3754   $28.38   $28.40   $28.40  
  Purchase #4 $150.40   8.625%   $163.372   $163.37   $163.35   $163.40  
  Purchase #5 $80.60   12.497%   $90.6726   $90.67   $90.65   $90.70  
  Purchase #6 $115.31   12.292%   $129.4839   $129.48   $129.50   $129.50  
  Purchase #7 $120.98   13.150%   $136.8889   $136.89   $136.90   $136.90  
  7 purchase totals = $746.99       $810.1542   $810.15   $810.20   $810.20