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 $231.70   13.102%   $262.0573   $262.06   $262.05   $262.10  
  Purchase #2 $211.54   11.270%   $235.3806   $235.38   $235.40   $235.40  
  Purchase #3 $185.34   11.480%   $206.617   $206.62   $206.60   $206.60  
  Purchase #4 $5.53   7.365%   $5.9373   $5.94   $5.95   $5.90  
  Purchase #5 $66.74   4.570%   $69.79   $69.79   $69.80   $69.80  
  Purchase #6 $33.37   5.826%   $35.3141   $35.31   $35.30   $35.30  
  Purchase #7 $202.29   11.290%   $225.1285   $225.13   $225.15   $225.10  
  7 purchase totals = $936.51       $1,040.2248   $1,040.23   $1,040.25   $1,040.20