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 $62.43   3.598%   $64.6762   $64.68   $64.70   $64.70  
  Purchase #2 $201.70   9.231%   $220.3189   $220.32   $220.30   $220.30  
  Purchase #3 $250.64   13.384%   $284.1857   $284.19   $284.20   $284.20  
  Purchase #4 $20.54   13.715%   $23.3571   $23.36   $23.35   $23.40  
  Purchase #5 $212.49   8.716%   $231.0106   $231.01   $231.00   $231.00  
  Purchase #6 $123.59   12.361%   $138.867   $138.87   $138.85   $138.90  
  Purchase #7 $160.38   3.868%   $166.5835   $166.58   $166.60   $166.60  
  7 purchase totals = $1,031.77       $1,128.9990   $1,129.01   $1,129.00   $1,129.10