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 $59.28   10.538%   $65.5269   $65.53   $65.55   $65.50  
  Purchase #2 $83.57   11.615%   $93.2767   $93.28   $93.30   $93.30  
  Purchase #3 $120.85   7.128%   $129.4642   $129.46   $129.45   $129.50  
  Purchase #4 $171.42   5.609%   $181.0349   $181.03   $181.05   $181.00  
  Purchase #5 $163.68   3.527%   $169.453   $169.45   $169.45   $169.50  
  Purchase #6 $191.90   7.614%   $206.5113   $206.51   $206.50   $206.50  
  Purchase #7 $11.47   6.321%   $12.195   $12.20   $12.20   $12.20  
  7 purchase totals = $802.17       $857.4620   $857.46   $857.50   $857.50