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 $153.47   4.759%   $160.7736   $160.77   $160.75   $160.80  
  Purchase #2 $114.74   11.408%   $127.8295   $127.83   $127.85   $127.80  
  Purchase #3 $144.87   11.581%   $161.6474   $161.65   $161.65   $161.60  
  Purchase #4 $148.97   13.667%   $169.3297   $169.33   $169.35   $169.30  
  Purchase #5 $199.34   9.748%   $218.7717   $218.77   $218.75   $218.80  
  Purchase #6 $53.36   9.366%   $58.3577   $58.36   $58.35   $58.40  
  Purchase #7 $138.27   6.564%   $147.346   $147.35   $147.35   $147.30  
  7 purchase totals = $953.02       $1,044.0556   $1,044.06   $1,044.05   $1,044.00