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 $81.33   4.864%   $85.2859   $85.29   $85.30   $85.30  
  Purchase #2 $217.33   10.272%   $239.6541   $239.65   $239.65   $239.70  
  Purchase #3 $6.64   10.644%   $7.3468   $7.35   $7.35   $7.30  
  Purchase #4 $178.76   4.641%   $187.0563   $187.06   $187.05   $187.10  
  Purchase #5 $157.80   11.107%   $175.3268   $175.33   $175.35   $175.30  
  Purchase #6 $203.97   12.641%   $229.7538   $229.75   $229.75   $229.80  
  Purchase #7 $250.54   13.307%   $283.8794   $283.88   $283.90   $283.90  
  7 purchase totals = $1,096.37       $1,208.3031   $1,208.31   $1,208.35   $1,208.40