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 $157.73   6.259%   $167.6023   $167.60   $167.60   $167.60  
  Purchase #2 $242.97   6.750%   $259.3705   $259.37   $259.35   $259.40  
  Purchase #3 $161.74   13.264%   $183.1932   $183.19   $183.20   $183.20  
  Purchase #4 $97.99   6.791%   $104.6445   $104.64   $104.65   $104.60  
  Purchase #5 $38.56   3.199%   $39.7935   $39.79   $39.80   $39.80  
  Purchase #6 $145.94   12.537%   $164.2365   $164.24   $164.25   $164.20  
  Purchase #7 $181.98   10.192%   $200.5274   $200.53   $200.55   $200.50  
  7 purchase totals = $1,026.91       $1,119.3679   $1,119.36   $1,119.40   $1,119.30