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 $75.82   10.606%   $83.8615   $83.86   $83.85   $83.90  
  Purchase #2 $111.80   9.242%   $122.1326   $122.13   $122.15   $122.10  
  Purchase #3 $147.29   6.187%   $156.4028   $156.40   $156.40   $156.40  
  Purchase #4 $207.27   12.198%   $232.5528   $232.55   $232.55   $232.60  
  Purchase #5 $167.28   3.649%   $173.384   $173.38   $173.40   $173.40  
  Purchase #6 $145.44   7.495%   $156.3407   $156.34   $156.35   $156.30  
  Purchase #7 $83.58   3.706%   $86.6775   $86.68   $86.70   $86.70  
  7 purchase totals = $938.48       $1,011.3519   $1,011.34   $1,011.40   $1,011.40