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 $206.35   12.106%   $231.3307   $231.33   $231.35   $231.30  
  Purchase #2 $41.78   5.183%   $43.9455   $43.95   $43.95   $43.90  
  Purchase #3 $127.93   4.423%   $133.5883   $133.59   $133.60   $133.60  
  Purchase #4 $156.92   7.852%   $169.2414   $169.24   $169.25   $169.20  
  Purchase #5 $203.77   4.226%   $212.3813   $212.38   $212.40   $212.40  
  Purchase #6 $181.68   9.830%   $199.5391   $199.54   $199.55   $199.50  
  Purchase #7 $154.65   6.746%   $165.0827   $165.08   $165.10   $165.10  
  7 purchase totals = $1,073.08       $1,155.1090   $1,155.11   $1,155.20   $1,155.00