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 $22.50   6.451%   $23.9515   $23.95   $23.95   $24.00  
  Purchase #2 $144.62   13.306%   $163.8631   $163.86   $163.85   $163.90  
  Purchase #3 $207.39   9.217%   $226.5051   $226.51   $226.50   $226.50  
  Purchase #4 $187.88   5.163%   $197.5802   $197.58   $197.60   $197.60  
  Purchase #5 $127.48   13.795%   $145.0659   $145.07   $145.05   $145.10  
  Purchase #6 $111.47   13.727%   $126.7715   $126.77   $126.75   $126.80  
  Purchase #7 $133.29   6.794%   $142.3457   $142.35   $142.35   $142.30  
  7 purchase totals = $934.63       $1,026.0830   $1,026.09   $1,026.05   $1,026.20